The United States of America is located in the middle of the North American continent. The 48 states of the conterminous United States stretch from the Atlantic Ocean in the east, where the country has a 6,000-km-long (3,700-mi) coastline--including the Gulf of Mexico--to the Pacific, where the coast stretches for 2,100 km (1,300 mi). The United States shares borders with only 2 other countries. In the north the border extends across the width of both Canada and the United States and between Alaska (the 49th state) and Canada for 8,900 km (5,500 mi); in the south the shorter border with Mexico is 3,111 km (1,933 mi) long. Hawaii (the 50th state) is composed of a group of Pacific islands about 3,400 km (2,100 mi) southwest of San Francisco; Alaska occupies the northwestern extremity of North America, with a 10,700-km (6,700-mi) coastline on the Pacific and Arctic oceans. The United States is the world's fourth largest country--after the Commonwealth of Independent States (the former \TUSSR\t), Canada, and China--and the fourth most populous (after China, India, and the former \TUSSR\t). The 50 states are blessed with a variety of mineral, agricultural, water, and other land resources that provide the basis for a highly productive economy--in fact, the United States is the world's wealthiest nation. For most of the 20th century the country has enjoyed economic preeminence throughout the world, particularly during the post-World War II era. Yet within the United States, the population, per capita wealth, and general welfare are unevenly distributed, with areas of affluence often contiguous with areas of poverty. Beginning in the early 1970s the United States faced economic difficulties brought on by a high foreign trade deficit, the declining value of the dollar abroad, high governmental spending, and inflation. During the 1980s, inflation was brought under control and tax-cutting stimulated economic expansion in some sectors, although there was stagnation in others. The trade deficit remained, however, and the national debt burgeoned as never before. By 1992 the nation was undergoing recession and economic difficulties in the manufacturing, savings and loan, banking, and insurance industries. The United States plays a prominent role in world affairs and is an influential member of such multinational organizations as the United Nations (headquartered in New York City) and the World Bank (headquartered in Washington, D.C.). For much of the post-World War II period the United States, a capitalist nation, found itself in opposition to the \TUSSR\t, the most powerful Communist country. Soviet reforms of the 1980s, the demise of the Soviet Communist party after a failed coup in 1991, and the break up of the Soviet Union have significantly reduced international tensions. The United States came into existence as a result of the \TAmerican Revolution\t (1775-83), during which the original thirteen states declared and won their independence from Great Britain. During the 19th century, while the European powers built worldwide empires, the young United States focused on expansion across the North American continent and on internal development. Nevertheless, the country gradually acquired some overseas territories, collectively known as the \TUnited States outlying territories\t, that it continues to administer. These include \TGuam\t and \TPuerto Rico\t (both acquired in 1899); \TAmerican Samoa\t (acquired in 1900); the \TPanama Canal Zone\t (acquired in 1904 but scheduled for return to Panama by the year 2000); and the U.S. \TVirgin Islands\t (acquired in 1917). The Trust Territory of the Pacific Islands (see \TPacific Islands, Trust Territory of the\t), was established in 1947. \TPalau\t, in the \TCaroline Islands\t, is its only remaining component. LAND AND RESOURCES The United States covers 9,372,571 sq km (3,618,770 sq mi), which divide into several large natural regions, each with unique topography, geology, and resources. Eastern United States Along the coasts of the Gulf of Mexico and the Atlantic Ocean northward to Long Island is a coastal plain, almost all of it below 100 m (300 ft) in altitude and with an average width of 160-320 km (100-200 mi). This coastal plain covers about 10% of the country's total land areas. Except for the muddy delta of the Mississippi River, the shores of the plain are sandy, most of them with barrier beaches surmounted by dunes and backed by shallow, muddy estuaries of brackish or salt water. These include marshlands, so-called wetlands, that are biologically important because they breed tremendous quantities of the primitive plants and animals that provide the basic food supply for all higher organisms living there. The coastal plain extends under the Gulf of Mexico and Atlantic Ocean, more than 320 km (200 mi) in places, where it forms the continental shelf. \TLong Island\t, \TMartha\t's \Tvineyard\t, \TNantucket Island\t, and Block Island are actually tops of coastal plain hills projecting above sea level. The coastal plain is the subject of conflicting interests among its fishing, shipping, petroleum, mineral resources, seashore recreation, and residential uses. Inland from the coastal plain, and almost parallel to the Atlantic coast, is the \TAppalachian Mountain\t system, which extends from Alabama and Georgia north to Canada; in New England the old rocks of the highlands extend to the coast and form rocky shores. The Appalachian Mountains divide into natural regions. To the east, bordering the Atlantic coastal plain, is a transitional zone, the \TPiedmont Plateau\t, which has elevations ranging from approximately 100 to 300 m (300 to 1,000 ft) above sea level. The boundary between the Piedmont and the coastal plain is an escarpment across which the rivers tumble in falls to the lower coastal plain. This \Tfall line\t marks the head of navigation, and cities of the urban corridor--such as Trenton, N.J., Philadelphia, Wilmington, Del., Baltimore, Md., Washington, D.C., and Richmond, Va.--are located on the Fall Line. In \TNew England\t are found the \TGreen Mountains\t, the \TWhite Mountains\t, and the \TBerkshire Hills\t. Farther south the mountain ridges of the \TBlue Ridge\t reach 2,037 m (6,687 ft) at Mount \TMitchell\t in North Carolina, the highest point east of the Mississippi River. West of the Blue Ridge is a hilly region called the Ridge and Valley Province, about 40-120 km (25-75 mi) wide. Farther west are the coal-rich, roughly dissected and mountainous Appalachian Plateaus; the easternmost portion, \TAllegheny Mountains\t (or Plateau), mostly between 300 and 1,000 m (1,000 and 3,300 ft) in altitude, rise up abruptly from the Ridge and Valley Province. Throughout the Appalachian Plateaus as a whole local relief commonly exceeds 500 m (1,600 ft). Moreover, the steep mountainsides are unstable, which makes coal mining difficult. To the west of the \TGreat Smoky Mountains\t, the Ridge and Valley Province separates them from the \TCumberland Plateau\t. Midwest The Appalachians give way to a central lowland and the \TGreat Plains\t that extend 1,600 km (1,000 mi) west to the Rocky Mountains and reach from Canada south to the Gulf coastal plain. Some highland areas in the Midwest are the \TOzark\t Mountains in Arkansas and Missouri, the Ouachita Mountains in Arkansas and Oklahoma, the \TMesabi Range\t in Minnesota, and the \TBlack Hills\t in South Dakota. The lowest part of the region is along the Mississippi River, at about 300 m (1,000 ft). West of the river the plains rise westward to the 1-mi-high (1.6-km) base of the Rocky Mountains. The northern section of the central lowlands has more irregular topography, partly because of its glacial debris. Rockies and Great Basin The \TRocky Mountains\t, extending northward from New Mexico into Canada, have many summit ridges higher than 3,000 m (10,000 ft), and many peaks reach above 4,250 m (14,000 ft). The highest point in the U.S. portion of the Rockies, Mount \TElbert\t, reaches 4,399 m (14,432 ft) in Colorado. The Rockies form a bold, east-facing mountain front--including the dramatic Front Range in Colorado--that was a major barrier to the westward expansion of the United States. In Wyoming the mountain ranges are isolated from one another by intermontane basins and plains. The Wyoming Basin was the main passage through the Rockies used by wagon trains traveling west. Beyond the Rockies are elevated plateaus. In the south is the \TColorado Plateau\t, averaging about 1,500 m (5,000 ft) above sea level. The plateau is cut by spectacular canyons, including the \TGrand Canyon\t of the Colorado River. To the north are somewhat lower lava plateaus along the Snake and Columbia rivers. West of the Colorado Plateau and south of the lava plateaus is the \TGreat Basin\t, part of the \Tbasin and range province\t. It consists of scores of closed desert basins containing playa, or ephemeral lakes, and separated by equally numerous rocky and mountainous ridges, most of which trend north-south. Most of the basins range between 1,200 and 1,500 m (4,000 and 5,000 ft) in altitude. The mountain ranges separating the basins are mostly 500 to 2,000 m (1,500 to 6,000 ft) higher. South of the Great Basin is a lower area also without exterior drainage and including \TDeath Valley\t and the \TSalton Sea\t, both below sea level. East of the Colorado River, more desert basins and ranges extend east to the Great Plains. The \TRio Grande\t, rising in southwestern Colorado and flowing south through New Mexico, connects several of these basins. West Coast Much larger basins and ranges form the Pacific Mountains. In California is the \TSierra Nevada\t, mostly a granite block, about 725 km (450 mi) long and 125 km (75 mi) wide. The highest peak, Mount \TWhitney\t, reaches 4,418 m (14,494 ft). In northernmost California and in Oregon and Washington the Sierra gives way to the volcanic \TCascade Range\t. Mount \TRainier\t reaches 4,392 m (14,410 ft). West of these mountains are broad, long basins--the Great Valley in central California and the valley of the \TWillamette River\t and Puget Trough in Oregon and Washington. The low parts of these basins are only a little higher than sea level. West of them are the \TCoast Ranges\t, which extend from California to Alaska. These ranges are only half as high as the Sierra and Cascades and form rocky headlands facing the Pacific Ocean. Sandy beaches are found mostly in coves between the headlands and at a few protected bays. Almost no continental shelf borders the Pacific coast. Alaska and Hawaii Alaska, whose area is equal to one-sixth of the area of the lower 48 states, consists of mountain ranges curving concentrically around the Gulf of Alaska and extending west in an arc forming the \TAleutian Islands\t. North America's highest point, Mount \TMcKinley\t (6,194 m/20,320 ft), is in the Alaska Range. North of these mountains is a broad plateau bisected by the Yukon River. North of it is the \TBrooks Range\t, the northern base of which slopes to the Arctic Ocean, including the oil-rich \TPrudhoe Bay\t area. Hawaii, the 50th state, located near the center of the Pacific Ocean, consists of volcanic islands aligned in a northwesterly direction. The volcanism is older and the islands are lower northwestward. Either the ocean crust is moving northwest across a hot spot, or the hot spot is moving southeast under the crust. Active volcanoes, \TKilauea\t and \TMauna Loa\t, are located on Hawaii, the southeasternmost island. Geologic Structure Like other continents, North America has a central nucleus called a shield. The \TCanadian Shield\t, as it is termed, is mostly in Canada but extends southward into the United States at Lake Superior. Shield rocks are more than 1 billion years old, and some are 4 billion years old. In the central lowland and Appalachian region, surrounding the exposed shield, is a stable platform, underlain by shield rocks but overlain by younger sedimentary rocks, averaging about 1,700 to 3,000 m (5,600 to 10,000 ft) thick. These sedimentary rocks are 1 billion to 225 million years old (late Precambrian and Paleozoic). Overlying these in the western part of the stable platform are younger sedimentary formations 60 to 150 million years old (Mesozoic). All these sedimentary rocks are generally almost horizontal; mountains are few--the \TBlack Hills\t, the southern Rockies, and mountains in Oklahoma and Arkansas are exceptions. The eastern and western edges of the stable platform were downwarped to form linear troughs thousands of kilometers long and hundreds of kilometers wide. These troughs (or geosynclines) were then flooded by seas. The trough along the eastern edge of the platform, the present-day site of the Appalachians, accumulated sediments approximately 12,000 m (40,000 ft) thick. West of the platform, at the site of the Great Basin, the geosynclines lasted longer and the sediments accumulated to thicknesses exceeding 30,500 m (100,000 ft). After formation of the troughs, the sides were squeezed together, and the sedimentary formations were folded, faulted, uplifted, and subsequently sculptured by erosion to form the mountains along the east and west sides of the continent. During the last 60 million years (the Cenozoic Era), the Atlantic and Gulf coastal plains were submerged and the western United States was uplifted in a broad arch extending from the Mississippi River to the Pacific. The basins and ranges developed largely by faulting of the previously folded and arched rocks. These crustal movements were accompanied by extensive volcanic activity that formed the lava plateaus along the Snake and Columbia rivers; the Cascade Range; the Coast Ranges in Oregon; features around the southwestern and southern edges of the Colorado Plateau; and other isolated eruptions in the Great Basin. Surface Deposits and Soils In the southeastern United States the ground is clayey and thick, in places deeper than 30 m (100 ft). The clay formed as a result of weathering that altered the minerals in hard rocks, even granite, to clay minerals. Iron was disseminated through the clay, staining it red, the characteristic color of such ground. Similar soil formed along the very wet northwest coast of the United States. In less humid parts of the country, weathering is less intense, mostly less than a meter deep, and the ground contains little clay. In humid regions, such as the Appalachians, 95% of the mountainsides are covered with colluvium--loose, weathered rock debris. Even in the Rocky Mountains more than 80% of the ground is covered with colluvium, although the deposits are thinner than in humid regions. Other extensive surface deposits include those of the Pleistocene glaciers that covered Canada and extended into the northern United States. They reached as far south as Long Island, northern Pennsylvania, the Ohio and Missouri rivers, and Puget Sound lowland. In hilly New England, the deposits are stony; on the plains, less so. Stones cleared from New England fields have been used to build the stone walls so characteristic of that region. In the central United States the glacial deposits and much of the country to the south are covered by wind-laid silt (loess). These deposits form some of the best agricultural land in the United States. They were produced as the Pleistocene glaciers melted, discharging floods southward, and as the floods ebbed, west winds blew dust clouds eastward from the channels. The deposits become thinner and finer grained eastward from the rivers. Although highly productive, these soils are subject to wind erosion and gullying. Winds have also built sand dunes, not only in the western deserts but on many lake shores, including those of the Great Lakes. Other surface deposits were laid down by streams, as alluvial floodplains in valley bottoms, and as fan-shaped deposits where valleys issue from mountains. Alluvial bottoms are fertile land and important sources of groundwater, although subject to pollution. They also are subject to flooding, as are alluvial fans. Lake deposits are numerous in glaciated areas, but they are most extensive in the desert depressions of the Great Basin. This seeming anomaly occurs because those basins collected meltwater from ice fields and glaciers in the mountains. Even Death Valley, where annual precipitation averages only about 38 mm (1.5 in), had a lake approximately 180 m (600 ft) deep. The east part of the Great Basin contained Pleistocene Lake Bonneville, which covered 52,000 sq km (20,000 sq mi) and had a maximum depth of 300 m (1,000 ft). \TGreat Salt Lake\t is a salt-brine remainder from that Pleistocene lake, as are the \TBonneville Salt Flats\t. Death Valley is now without a lake but has a salt pan. Despite 40 years of conservation education and other efforts, no more than 25% of U.S. farmlands are managed according to approved soil-conservation practices. The United States continues to deplete its soil resources by erosion and loss of organic matter. Climate Most of the United States has a continental climate, characterized by considerable annual variability. Coastal regions, moderated by the oceans, have less variable climates; Hawaii has slight variability, with most of the variation due to elevation. Alaska is partly cold-wet and partly cold-dry. Much of the northern half of the state is permanently frozen, in places to depths as great as 300 m (1,000 ft). The eastern United States is humid, with annual precipitation averaging more than 500 mm (20 in). The western part of the country--beginning approximately at 100 deg west longitude--except for the mountains and the maritime Pacific coast, is mostly semiarid with annual precipitation averaging between 250 and 500 mm (10 and 20 in), but parts are arid with annual precipitation averaging less than 250 mm (10 in). The western mountains receive about 500 mm (20 in) of precipitation yearly. The northwestern coast receives more than 2,500 mm (100 in) of precipitation each year. A traverse eastward across the United States illustrates the importance of seasonal differences in precipitation. Along the Pacific coast precipitation occurs mostly during the winter. In the central United States it is greatest during the summer growing season, further contributing (along with the rich soils) to the agricultural productivity of that region. In eastern states precipitation is rather even throughout the year. The traverse also shows that precipitation is greatest at the mountains and least to the leeward of them. The country's temperatures are as varied as precipitation and are heavily influenced by latitude, with longer and colder winters farther north. Temperatures are also influenced by proximity to the oceans. In the northeastern part of the country the average annual temperature in New York is 13 deg C (55 deg F). Farther south is a subtropical zone: Charleston, S.C., has an average annual temperature of 19 deg C (66 deg F). The only tropical zone of the United States occurs in southern Florida, and Miami experiences an average temperature of 24 deg C (75 deg F). In the central United States the continental climate is not moderated by the ocean, and seasonal differences are more extreme. In Minneapolis, Minn., the average temperature is 7 deg C (45 deg F), whereas in Tulsa, Okla., only about 2 deg farther west but 1,030 km (640 mi) south, the temperature averages 16 deg C (61 deg F). Along the west coast, temperatures, moderated by the ocean, are mild. Portland, Oreg., has an average annual temperature of 12 deg C (54 deg F); Los Angeles, in the Mediterranean climate zone, experiences a temperature of 17 deg C (63 deg F). Climate hazards in the United States include hurricanes along the Gulf and Atlantic coasts, tornadoes in the southeast and central states, hail on the western plains, dry electric storms that cause forest fires on western mountains, floods in the central and eastern states and along the Pacific coast in winter, and droughts in most of the western states. Rivers and Lakes Inland water covers about 200,000 sq km (78,500 sq mi), or almost 2% of the total area of the United States. The \TMississippi River\t, flowing south across the eastern half of the conterminous United States, is major both in length (3,779 km/2,348 mi) and in annual discharge (18,200 cu m per sec/650,000 cu ft per sec). By contrast, the \TColorado River\t (Colorado) is about one-third as long as the Mississippi River system, but its average annual discharge is only 2% as great. An area along the Atlantic seaboard, only slightly larger than the Colorado River basin, has 20 rivers--including the \TConnecticut River\t, \TDelaware River\t, \THudson River\t, and \TSusquehanna River\t--each only one-third as long as the Colorado but together discharging 20 times as much as the Colorado. In terms of discharge, the major rivers, in addition to the Mississippi, are the \Tsaint\t \TLawrence\t \Triver\t, \TOhio River\t, \TMissouri River\t, \TColumbia River\t, and \TSnake River\t. The \TYukon River\t is Alaska's principal river. Where annual precipitation averages less than 500 mm (20 in), even main streams are mostly ephemeral, flowing only when there are wet seasons or local storms. Water supplies in those areas, to a considerable degree, must be obtained from groundwater, and in parts of the arid southwestern states withdrawals (mostly for irrigation) have caused groundwater levels to fall alarmingly in places, enough to cause localized subsidence of the land surface and even damage to buildings. Lakes and peat bogs are numerous in the glaciated parts of the United States, especially in northern Minnesota. The lakes are small and used primarily for recreation, but the \TGreat Lakes\t are important arteries of transportation. Florida has lakes and bogs at limestone sinks, including Lake \TOkeechobee\t. The troughs of the Great Basin have ephemeral lakes. A few permanent ones are located at the eastern foot of the Sierra Nevada. The Salton Sea and Great Salt Lake are saline. Many of the lakes, especially in the west, have been created by dams; Lake \Tmead\t has the greatest capacity. Vegetation With such varied climate and topography, it is hardly surprising that the vegetation of the United States is equally varied. In Florida the subtropical vegetation includes mangrove and palmetto. Farther north in the southeastern states, forests of loblolly and slash pines grade north near the Tennessee River to hardwood forest with oak and hickory. In the Great Lakes region a different pine forest--of white pine--appears, and north of this are fir and spruce. In Alaska, north of the spruce zone, is tundra. These differences northward reflect decreasing temperature, especially shortening of the growing season. More striking differences occur between the humid east and the arid west. Hardwood forest extends westward beyond the Mississippi River, giving way to grassland on the plains. Rocky Mountain forests are chiefly coniferous, with pine and Douglas fir near the base and spruce and true fir extending upward to the timberline (3,500 m/11,500 ft in the Southern Rockies). Above that the growing season is too short for trees. West of the Rockies, on the plateaus and in the Great Basin, desert shrubs occur, with patches of woodland or forest on the isolated mountain ranges. These western mountains have two timberlines, one at high altitude because of the cold and the other near the mountain base, below which trees cannot grow because of insufficient precipitation. Forests rather like those in the Rockies grow on the eastern slopes of the Sierra Nevada and the Cascades; the western slopes have evergreen oaks with Douglas fir and, on the Sierra Nevada, sequoia. The central Coast Ranges have redwood, grading north to Douglas fir and spruce, and grading south to a scrubby growth known as chapparal. Resources Agriculturally, the United States is richly productive, with many crops providing a surplus for export. Most of the eastern two-thirds of the conterminous United States is arable; the land of the western United States is used mostly for grazing but has considerable irrigated lands for crops. The principal U.S. crops are: fruit, truck farming products, and special crops (including rice and sugarcane) along the Gulf coast, in irrigated areas of the west, and near urban areas in the east; cotton in the southeastern states and on some irrigated lands in the west; tobacco, peanuts, fruit, and general farm products on the Atlantic coastal plain and in the eastern Appalachians; dairy products and hay in the northern states; and corn, wheat, and soybeans on the plains. Livestock on farms habitually totals over 100 million cattle and additional millions of hogs and sheep and hundreds of millions of chickens and turkeys. The grazing capacity of the land is very unequal. The humid half of the country can support as many as 500 cows per year per sq mi (193 per sq km) whereas the semiarid and arid western half can support fewer than 100 per sq mi (40 per sq km) and some parts support only about 10 head per sq mi (4 per sq km). Commercial forests cover more than 2,000,000 sq km (800,000 sq mi), especially in the northwestern, northern midwest, and the southeastern states. They produce, besides lumber, paper pulp, resins, and syrup. The annual forest cut and burn is less than the growth, but care is needed to minimize water and erosion losses due to grazing and lumbering. In recent years increased recycling of paper is reducing consumption of paper pulp. Changing interests in water resources are reflected in the history of water management. First, the need for transportation led to the building of canals, such as the \TErie Canal\t, in the eastern states in the early 19th century. Second came the great period of flood control, especially along the Mississippi River. Third came a period of large-scale development of irrigation systems in the west, beginning around the turn of the century. Fourth came a period of developing hydroelectricity, beginning during the 1930s. Today's principal concern is pollution control. In the future will come a stage when controls will be needed to prevent groundwater withdrawals from exceeding recharge. Mineral production, although less than 5% of the gross national product (\TGNP\t), is vitally important. No nation is self-sufficient in minerals, and although the United States has more than its share, nevertheless domestic production of many minerals is less than demand, necessitating imports. Fossil-fuel shortages combined with high demand threatens the United States with severe economic problems. Alternate sources of energy such as solar, geothermal, and wind energy are in the early stages of development. PEOPLE Prior to the discovery (1492) of the New World by Christopher Columbus the area of the United States had an Indian population averaging only about 1 person per 13 to 26 sq mi (roughly 1 person per 5 to 10 sq mi). When George Washington was president in 1790 the population had grown to almost 4,000,000; only 5 cities had populations exceeding 10,000. During the next 100 years the population doubled 4 times--to about 8 million in 1815, to 16 million in 1840, to 32 million in 1861-62, and to 64 million in 1890. By 1990 the population had reached nearly 250,000,000. Ethnic Composition In 1990 the native American population (see \TIndians, American\t; \TEskimo\t; and \TAleut\t) totaled more than 1.9 million. Of the Indians, who constitute the overwhelming majority, about half live on or near some 300 reservations. There they engage in farming and sheepherding and excel in such crafts as pottery making, rug and basket weaving, silversmithing, and beadwork. Most reservation land is located in Arizona, New Mexico, Utah, South Dakota, Washington, and Montana. The half of the Indian population off reservations live mostly in cities, especially in the north, central, and western states and in Alaska. About 12.1% of the total population--29,986,060 persons (1990 census)--are African Americans, almost all descendants of slaves. Slightly more than half are concentrated in the southern and southeastern states, the remainder in urban centers of the northeast, north central, and Pacific states. Black migration during the 1980s was away from northern industrial centers and toward metropolitan areas of the South and West (see \Tblack Americans\t). The vast majority of Americans, however, are descended from Europeans who were attracted to the United States by religious and political freedom and economic opportunities. During the colonial period most settlers came from the British Isles and settled along the eastern seaboard; the French settled the St. Lawrence River valley. The first great \Timmigration\t wave--from 1820 to 1860--saw the arrival of more than 5 million new Americans. Of these, 90% were from England, Ireland, and Germany. By the middle of the 19th century the culture and customs of western Europe dominated the United States from coast to coast. After the Civil War, immigration increased dramatically; between 1860 and 1920, about 29 million persons arrived. The composition of the immigrant population had shifted, and most came from eastern and southern Europe--Russia, Poland, the Balkans, and Italy. Unlike many earlier immigrants, they remained in the eastern states and industrial midwestern states such as Michigan and Illinois, usually settling in the cities, rather than continuing west. During the same period increasing numbers of Asians, especially Chinese and Japanese, migrated to the Pacific coast and to Hawaii. These immigrants tended to form ethnic enclaves within the predominantly western European communities (see \TAsian Americans\t). Asian and Pacific Islanders in the United States total 7,273,662 (1990 census). The white immigrants, on the other hand, mixed to a considerable degree with the earlier western European stocks, beginning the so-called American melting pot. The mixing process was facilitated by the public school system. In the southern part of the country, where most blacks lived, however, the races were segregated until the middle of the 20th century, and although diminishing, de facto segregation remains a national problem. The total population of Spanish origin in the United States is 22,354,059 (1990 census). From 1980 to 1990 the Hispanic population grew by 53%, making it the second-fastest-growing ethnic group (after the Asian population, which grew by 107.8%). In southern Texas, New Mexico, Arizona, and southern California, a considerable percentage of the population is of Mexican-American origin (see \TChicano\t). Each year thousands more enter the United States, most illegally, because of overpopulation in Mexico and greater opportunities in the United States. The arrivals do not settle near the border where employment is limited but migrate to the interior of the United States, especially to urban areas. The eastern states have also experienced an influx of Spanish-speaking immigrants from Central America and the Caribbean. Most live in the cities, especially New York and Miami. (See also \THispanic Americans\t.) Religion About 56% of all Americans give their religious affiliation as Protestant, with Baptists outnumbering members of other individual denominations, including those of the Methodists, Lutherans, Presbyterians, Episcopalians, Latter-day Saints, Pentacostalists, Churches of Christ, and United Church of Christ. About 28% of the U.S. population are Roman Catholic. A small percentage belong to Eastern Orthodox churches, and about 2% are Jewish. Other major world religions--Buddhism, Hinduism, Islam, and the tribal religions, notably from Africa--are lightly represented in the United States. Demography The annual rate of population increase in the United States is nearly 1% (1980-90). In 1990, about three-quarters of the total population lived in urban, including metropolitan, areas. Thirty-nine cities had more than 1 million inhabitants in the metropolitan areas, and 24 cities had more than 500,000 residents in the city center: \TBaltimore\t, \TBoston\t, \TChicago\t, \TCleveland\t, \TColumbus\t (Ohio), \TDallas\t, \TDetroit\t, \TEl Paso\t, \THouston\t, \TIndianapolis\t, \TJacksonville\t, \TLos Angeles\t, \TMemphis\t, \TMilwaukee\t, \TNashville\t, \TNew York\t, \TPhiladelphia\t, \TPhoenix\t, \TSan Antonio\t, \TSan Diego\t, \TSan Francisco\t, \TSan Jose\t, \TSeattle\t, and \TWashington, D.C\t. Urban problems have developed in many U.S. cities because large numbers of the more affluent whites have moved out of the city centers to the suburbs. Much light industry and other businesses have followed them. Thus many large cities are faced with decaying downtown and residential areas--often primarily the home of blacks and Hispanics. As a consequence the tax base of many cities has been eroded, and almost every major city faces financial difficulties. In 1990 the country's overall population density was 27 persons per sq km (70 per sq mi), but great regional variations exist: New Jersey has the highest density among the 50 states; the lightest density in the lower 48 states is in Wyoming, although Alaska has the least density of any of the states. During the 1980s, Iowa, North Dakota, West Virginia, and Wyoming lost population, and various other states, many in the northeastern and midwestern regions experienced only a minuscule rate of growth. The fastest-growing states were Nevada, Alaska, Arizona, Florida, California, and New Hampshire. The birthrate in the United States is 15 per 1,000 inhabitants (1990), a figure about equal to Canada's but higher than that of most of Western Europe. The death rate, 9 per 1,000 inhabitants, is about equal to, or a bit lower than, that of the other industrialized nations. Health and Education In the late 1980s the United States had more than 6,800 hospitals and an average of 5.3 hospital beds for every 1,000 inhabitants. About 586,000 physicians were practicing. Female residents of the United States have a life expectancy of about 80 years at birth, whereas for males it is 73 years. The average life expectancy at birth for all whites is 75.5 years; for blacks, however, it is 69.5 years, although it has increased from 45 years in 1920. The nation's infant mortality rate is 10 per 1,000 live births. Although this is one of the world's lowest rates, it is surpassed by that of several European nations, especially Scandinavian countries. Illiteracy has been almost eliminated in the United States. The median school years completed by U.S. citizens 25 years and older was 12.7 years. Approximately 20% of all Americans have 4 years or more of college. Education is required between the ages of 5 and 16. Public primary and secondary education is mostly locally funded. In 1988, 42 million pupils attended public elementary and secondary schools; 6.1 million students attended private schools. Of the nation's institutions of higher education, about 60% are 4-year institutions, and the remainder are 2-year schools. Privately operated institutions include many of the nation's most prestigious universities and colleges. Together they enroll about 20% of all higher-education students. Public institutions enroll about 80% of all higher-education students, and each state operates a university system. Beginning in the 1960s, 2-year institutions grew most rapidly; many of these community colleges are operated by counties and municipalities. For a more detailed description of the country's educational system, see \TUnited States, education in the\t. Communications In 1721 the New England Courant began publication in Boston. By 1990 there were 1,626 daily newspapers published in the United States, a number of them in languages other than English. The daily newspapers had a total circulation of nearly 62,500,000 (1989). Among the best-known of the dailies with circulations exceeding 500,000 are the \TChicago Tribune\t, \TNew York Times\t, \TWashington Post\t, and the Los Angeles Times; the \TSt. Louis Post-Dispatch\t, Atlanta Constitution, Miami Herald, and Toledo Blade are also important. The \TChristian Science Monitor\t, \TWall Street Journal\t, and \TUSA\t Today are the principal nationally circulated dailies. The country is served by 4,932 AM and 4,155 FM radio stations (1988). There are about 200 million television sets in the United States and nearly 1,100 broadcast commercial stations. Besides broadcast commercial dominated by a few national networks, there are 9,050 (1989) cable systems and 305 (1986) public-television stations in operation. Also a smaller fourth network, Fox, began broadcasting in 1986. ECONOMIC ACTIVITY Economic Development During the colonial period, after establishing subsistence farms along the Atlantic seaboard, the pioneer settlers developed a maritime and shipbuilding industry. Forests provided the timbers needed for ships and homes. Until after the middle of the 19th century wood also was the nation's principal source for fuel, and wood ashes produced potash. The submerged part of the coastal plain off the New England coast at Georges Bank was and remains one of the world's great fishing areas, especially for herring, mackerel, and cod, and the shores yielded lobsters, crabs, and shellfish. Whaling was important during colonial times but declined after the mid-19th century. Other economic activities in the eastern United States related to water navigation included development of steamboats and construction of canals around waterfalls and rapids to permit access by water to the Appalachians and the Ohio River. During the early 19th century the falls were also used to develop power for mills in the early stage of the Industrial Revolution. Mineral resources along the Eastern Seaboard were meager. Salt was produced from seawater at evaporating pans. Iron ore was obtained from bogs. Coal was produced from early Mesozoic formations near Richmond, Va. Manufacturing and other industries became increasingly important when coal became plentiful because of improved roads, canals, and newly built railroads that followed the westward migration. Where iron and coal could be economically joined, the giant steel industry developed, as at Pittsburgh and west to Chicago. Political and social changes affected the economy too. The Civil War freed the slaves, but high prices for cotton led to borrowing to hire labor. Collapse of the market brought ruin to the old plantation system and led to an era of small farms. As settlements and transportation lines spread across the central states, copper and iron were produced in the Lake Superior region. The great asset of the central United States, however, was and remains agricultural. The mechanized plow and harvester were invented to reap the produce of the vast fields there, as was barbed wire (1873) for fencing the plains farther west where trees are scarce. In the 1860s the railroads developed refrigerator cars. Agricultural products from the Midwest provided the basis of food-processing industries, such as flour milling in Minneapolis and Milwaukee. The Rocky Mountain states were first explored and exploited by fur traders during the two decades preceding the Civil War. Gathering furs had started in New England and spread westward across the Great Lakes region--first by the French, later by the \THudson's Bay Company\t for England, and then by American trappers and traders farther west and south, some working for companies such as John Jacob Astor's \TAmerican Fur Company\t (see also \Tfur trade\t). When gold was discovered (1848) in California, trappers already had blazed the way. The extensive and varied mineral deposits of the Rocky Mountains were discovered following the California \Tgold rush\t. The economy of the western United States today is based on livestock; irrigated farming; lumbering; metal mining (especially copper and molybdenum); energy resources (including oil, gas, coal, uranium, and hydroelectricity); transportation by railroad, highways, air, and pipelines and by shipping along the Pacific coast; manufacturing; offshore fisheries; and outstanding recreational attractions. More than two-thirds of the country's national parks are in the West. Alaska's economy depends chiefly on fisheries, oil, and recreation. Hawaii produces pineapples, sugarcane, and nuts but depends primarily on income from the large military and naval bases there and from tourism. Contemporary Economy In the late 1980s the gross national product (\TGNP\t) of the United States reached more than $5 trillion, the highest in the world. The per-capita income of more than $21,000 is also among the world's highest. Agriculture, fishing, and forestry together employ less than 3% of the total labor force, and contribute about 2% of the \TGNP\t. The leading crops, in order of value, are corn, soybeans, wheat, hay, cotton, tobacco, sorghum, rice, and potatoes. Most livestock is produced in the West and Midwest. The United States is the world's leading producer of soybeans and corn, and among the leading producers of meat, wheat, tobacco, hogs, and cattle. Forests cover about 2,960,000 sq km (1,142,862 sq mi), and of that total about two-thirds is timberland. Cut timber yields a value of about $1 billion annually. Income from the U.S. fishing industry was $3.5 billion in 1988. The Pacific states--especially Alaska and California--lead the nation in the value of their catch; Louisiana, on the Gulf coast, is also a leading producer. Almost one-fifth of the labor force is engaged in manufacturing, and industry contributes about the same proportion to the \TGNP\t. In the late 1980s the value added by manufacturing was more than $1 trillion. The leading industries in terms of value are transportation equipment, electric and electronic machinery, food and related products, nonelectrical machinery, chemicals, fabricated metal products, paper and related products, instruments and related products, primary metals, and rubber and plastic products. The large corporation dominates manufacturing in the United States, and in 1988 the 100 largest industrial concerns held nearly 75% of manufacturing assets. The United States is a world leader in production and export in various types of machinery, including office and telecommunication equipment; in transportation equipment, such as automobiles; in industrial raw materials; and in chemicals. In 1987 the United States produced 2.7 trillion kW h of electricity, the highest in the world. Of that total, 57% was derived from coal; lesser amounts were derived from petroleum, natural gas, nuclear power, and hydroelectricity. Some of the petroleum used for energy production is imported. The country's total installed capacity is 723.9 million kW (1988). Mining accounts for only about 2% of the \TGNP\t but produced $123.8 billion in 1987, nearly 80% of which was derived from mineral fuels--coal, natural gas, and petroleum. The principal minerals, in terms of value, are petroleum, natural gas, coal, stone, portland cement, sand and gravel, copper, gold, iron ore, clay, phosphates, lime, salt, sodium carbonate, boron minerals, sulfur, uranium, silver, masonry cement, lead, and zinc. As in the other highly developed countries--the so-called postindustrial nations--the service sector, widely defined, in the United States employs the great bulk of the labor force (about 70%) and produces the largest percentage of the \TGNP\t (also about 70%). Over 80.3 million persons work (1988) in transportation and public utilities; wholesale and retail trade; finance, insurance, and real estate; and services such as hotels, communications, and health care, as well as government. Together they produced $3.25 trillion. Tourism is also an important industry. In 1988, 12.5 million foreign tourists visited the country. Among foreigners and Americans alike, the National Park Service sites, including 50 national parks and 79 national monuments, are the favorite destinations. Major cities--including New York, Los Angeles, and Miami--are also important tourist magnets. As recently as 1975, U.S. exports were 10% greater than imports. Almost 20% of this international trade was with Canada; 17% was with other Western Hemisphere nations; about 25% was with Western European countries; and trade with Japan aggregated less than 10% of the total. In the 1980s, however, the trade balance reversed, sparked by large increases in the cost of petroleum imports; the value of imports of petroleum and petroleum products increased from $1.3 billion in 1970 to $62 billion in 1980. In 1990 the U.S. trade deficit was about $122.7 billion. In addition to petroleum, principal imports are automobiles, nonelectrical machinery, electrical equipment, consumer goods, and food. The principal industrial exports are machinery, transportation equipment, and chemicals; soybeans and corn are leading agricultural exports. In the late 1980s the United States had more than 6.2 million km (3.85 million mi) of roads, including more than 88,000 km (54,681 mi) of expressways. Rail tracks totaled 278,245 km (172,893 mi) in 1988. Of all passenger traffic in 1988, 81% was by private automobile, 18% by air, and only 0.7% by rail. During the same year, however, 37% of freight was carried by rail and 25% by motor vehicles. Leading U.S. seaports include New York, New Orleans, Houston, and Baton Rouge, La. Pittsburgh and Saint Louis are leading inland ports. GOVERNMENT The United States has a democratic government, meaning that it is "elected by the people and for the people." Every adult (aged 18 and over) can vote, yet only about 55% of the eligible voters exercise this right. Voters usually choose between the two political parties that dominate U.S. politics--the \TDemocratic party\t and the \TRepublican party\t. The country has a federal system of government in which power is divided between the national, or federal, government and the governments of the 50 states. A third level of government is provided at the local level by municipal and county authorities. Theoretically, the responsibilities of the different levels are delineated in the federal (see \TConstitution of the United States\t) and state constitutions, although actually the responsibilities overlap. The federal government and each of the 50 state governments are divided into three branches--executive, legislative, and judicial. Municipal and county governments are more varied but to a considerable degree are patterned after the federal and state models. The executive branch of the federal government is headed by the president (see \Tpresident of the United States\t) and vice-president, elected every 4 years. The administrative duties of the executive branch are divided among 14 departments: State, Treasury, Defense, Justice, Interior, Agriculture, Commerce, Labor, Health and Human Services, Housing and Urban Development, Transportation, Energy, Education, and Veterans Affairs. Numerous federal agencies, including those for regulation of the private sector (see \Tgovernment regulation\t), supplement the activities of these departments. The secretary of each department sits on the cabinet, the president's principal advisory body. The legislative branch of the federal government--the \TCongress of the United States\t--consists of a 100-member \TSenate\t, with 2 senators elected from each state, and a \THouse of Representatives\t, with 435 elected members, one for approximately every 560,000 persons. Reapportionment for the latter occurs every 10 years. Senators serve 6-year terms and representatives serve for 2 years. All budget appropriations originate in the House of Representatives, but the Senate must concur. Presidential appointees are confirmed by the Senate. The Senate also has the responsibility of approving treaties with foreign governments. Similarly, most states have 2 legislative bodies, although Nebraska has a unicameral body of 49 members. The chief executive of each state is the \Tgovernor\t. The federal judicial branch consists of the \TSupreme Court of the United States\t--the nation's highest judicial body--with a chief justice and eight other members appointed by the president with the advice and consent of the Senate; and 90 district courts, at least one in each state. They consider violations of federal law and certain civil cases involving persons in different states. Decisions may be appealed to the 12 U.S. appellate courts. Each state has a system of courts paralleling the federal system. State and local governments have responsibility for such local services as water supply, waste disposal, police and fire protection, hospitals and health, parks and recreation, schools, and libraries, but to a considerable degree each of these activities is shared by all levels of government including the federal government. The federal government alone has responsibility for national defense, but even this responsibility is shared with the states to the degree that each state has a national guard or militia. Charles B. Hunt Bibliography: DESCRIPTION, \Tgeography\t, AND \Tphysiography\t: Birnbaum, Stephen, ed., United States, 1987 (1986); Callison, Charles, ed., America's Natural Resources, rev. ed. (1967); Eardley, Armand J., Structural Geology of North America, 2d ed. (1962); Hunt, Charles B., Natural Regions of the United States and Canada (1974) and Physiography of the United States (1967); Landi, Val, The Bantam Great Outdoors Guide to the United States and Canada (1978); Least Heat Moon, William, Blue Highways (1983); Paterson, J. H., North America: A Geography of Canada and the United States, 7th ed. (1984); Pirkle, E. C., and Yoho, W. H., Natural Landscapes of the United States, 3d. ed. (1982); Ruffner, James, ed., Climates of the States, 2 vols. (1976); U.S. Geological Survey, The National Atlas of the United States of America (1970); Watson, J. Wreford, The United States (1983); White, C. L., et al., Regional Geography of Anglo-America (1985). \TPeople\t AND \Tculture\t: Boorstin, Daniel, The Americans, 3 vols. (1958-73; repr. 1984-85); Cohen, Wilbur J., and Westoff, Charles F., Demographic Dynamics in America (1977); Commager, Henry Steele, The Empire of Reason: How Europe Imagined and America Realized the Enlightenment (1977; repr. 1984); Dinnerstein, Leonard, Ethnic Americans: A History of Immigration and Assimilation (1975); Douglas, Ann, The Feminization of American Culture (1977); Gordon, Milton, Assimilation in American Life: The Role of Race, Religion and National Origins (1964); Highan, John, and Conklin, Paul K., eds., New Directions in American Intellectual History (1980); Hodgson, Godfrey, America in Our Time (1976); Lapham, L. H., Money and Class: Notes and Observations on the American Character (1988); Lasch, Christopher, The Culture of Narcissism: American Life in an Age of Diminishing Expectations (1979); Mulder, John M., and Wilson, John F., Religion in American History (1978); Pells, Richard H., The Liberal Mind in a Conservative Age (1985); Rhodes, Richard, Looking for America (1979); Roueche, Berton, Sea to Shining Sea (1986); U.S. Bureau of the Census, Statistical Abstract of the United States (annual). \Teconomics\t: Adams, Walter, The Structure of American Industry, 7th ed. (1985); Bruchey, Stuart, The Wealth of the Nation: An Economic History of the United States (1987); Duffy, James H., Domestic Affairs: American Programs and Priorities (1979); Hacker, L. M., The Course of American Economic Growth and Development (1970); Handlin, Oscar and Mary, The Wealth of the American People: A History of American Affluence (1975); Kirkland, Edward C., A History of American Economic Life, 4th ed. (1969); Porter, Glenn, Encyclopedia of American Economic History, 3 vols. (1980); Rodger, Harrell R., Poverty amid Plenty: A Political and Economical Analysis (1979); Rodgers, Harrell R., Poor Women, Poor Families (1986); Tufte, Edward R., Political Control of the Economy (1978; repr. 1980). \Tforeign policy\t: Belfiglio, Valente J., American Foreign Policy, 2d ed. (1983); Combs, Gerald, Brief U. S. Foreign Policy (1986); Crabb, C. V., Jr., American Diplomacy and the Pragmatic Tradition (1989); DeConde, Alexander, ed., Encyclopedia of American Foreign Policy, 3 vols. (1978); Hughes, Barry B., et al., Energy in the Global Arena (1985) and The Domestic Context of American Foreign Policy (1978); Isaak, Robert A., American Democracy and World Power (1977); Muravchik, Joshua, Exporting Democracy: Fulfilling America's Destiny (1991). \LPolitic\ls AND \Tgovernment\t: Adrian, Charles R., Governing Our Fifty States and Their Communities, 4th ed. (1978); Armbruster, M. E., The Presidents of the United States and Their Administrations from Washington to the Present, 7th ed. (1981); Council of State Governments, The Book of the States (biennial); Freeman, Roger A., The Growth of American Government (1975); Geiger, Theodore, The Future of the International System: The United States and the World Political Economy (1988); Janowitz, Morris, The Last Half-Century: Societal Change and Politics in America (1978); Johnson, Donald B., comp., National Party Platforms, 2 vols. (1978); Kelly, Robert, The Cultural Pattern in American Politics, vol. 1, The First Century (1979); Lees, John D., The Political System of the United States, rev. ed. (1983); Nye, Joseph S., Jr., Bound to Lead: The Changing Nature of American Power (1990); Office of the Federal Register, United States Government Manual (annual); Sohner, Charles P., and Martin, Helen P., American Government and Politics Today, 4th ed. (1984); Vidich, Arthur, and Bensman, Joseph, American Society: The Welfare State and Beyond, rev. ed. (1986). See also: \TAmerican art and architecture\t; \TAmerican literature\t; \TAmerican music\t; \TNorth America\t; and separate articles on each U.S. state, important cities, and major land features.