Mississippi system (incl. Missouri, Ohio, Platte, Red, Arkansas), Colorado, Columbia, Rio Grande.

Great Lakes in N (U.S.-Canada boundary runs through Ontario, Erie, Huron, and Superior; Michigan is wholly within boundary); Great Salt in Utah and Okeechobee in Florida.

Appalachian system (incl. White Mts. and Green Mts. in New England, Adirondacks and Catskills in New York, Blue Ridge and Great Smoky Mts. in SE), Ozark Plateau in Missouri, Arkansas, and Oklahoma, Rocky Mts. across (N to S) the W (incl. Bitterroot Range in N, Wasatch, Uinta, and Front ranges in cen. part), and ranges along Pacific coast (Cascade Range, the Sierra Nevada, and Coast Ranges); highest point Mt. McKinley, Alaska, 20,320 ft. (6194 m.); lowest point Death Valley, California, 282 ft. (86 m.) below sea level; highest point (excluding Alaska) Mt. Whitney, California, 14,495 ft. (4418 m.); highest point E of Mississippi River Mt. Mitchell, North Carolina, 6684 ft. (2037 m.).

Hawaii, Kodiak, Prince of Wales, Chichagof, St. Lawrence, Admiralty, Nunivak, Unimak.

Corn, wheat, soybeans, cotton, tobacco, oats, barley, rice, sugar beets, fruit; dairy products; livestock raising, fishing, lumbering; iron ore, coal, oil, natural gas, copper, zinc, sand and gravel, phosphate rock, gold; manufacturing: iron and steel, transportation equipment, machinery, chemicals, electronic equipment, textiles, paper; food products.

New York, Los Angeles, Chicago, Houston, Philadelphia, Phoenix, San Diego, Dallas, San Antonio.

Houston, New Orleans, Corpus Christi on Gulf of Mexico; New York, Norfolk, Philadelphia on the Atlantic; Valdez, Long Beach, Los Angeles on the Pacific; Baton Rouge, Pittsburgh, St. Louis on rivers.

Divided into 50 states and Washington, D.C. (for further details, see their individual entries).

Area orig. inhabited for several thousand years by numerous Indian peoples who had probably emigrated from Asia; European exploration and settlement from 16th cent. a.d. began displacement of Indians who also suffered severely from exposure to European diseases; first permanent European settlement, Spanish, at St. Augustine, Florida, 1565; English settlements in Virginia 1607, Massachusetts 1620, Maryland 1634, Pennsylvania 1681; English defeat of French in French and Indian War (1754–63) assured British political control over 13 colonies. Political unrest caused by English colonial policy culminated in American Revolution 1775–83 and Declaration of Independence 1776. U.S. organized first under the Articles of Confederation 1781 and finally under the Constitution 1787 as a federal republic. Purchased Louisiana region from France 1803; fought War of 1812 with Great Britain; acquired Florida from Spain 1819; established U.S. foreign policy with announcement of Monroe Doctrine 1823. In 1830 legalized removal of American Indians to lands W of Mississippi River, extended settlement into Far West mid-19th cent., esp. after discovery of gold in California 1848; annexed Texas 1845; established NW boundary by treaty with Great Britain 1846; secured New Mexico and California regions from Mexico 1848 by Treaty of Guadalupe Hidalgo ending Mexican War; acquired S Arizona from Mexico by Gadsden Purchase 1853. Disunified by conflict bet. slavery-based plantation economy in South and free industrial and agricultural economy in North, culminating in Civil War 1861–65 and abolition of slavery under Thirteenth Amendment. After reconstruction of union (1865–77), experienced rapid growth, urbanization, industrial development, and European immigration; in 1887 authorized allotment of Indian reservation land to individual tribesmen, resulting in widespread loss of land to whites; upheld racial segregation 1896 by declaring “separate but equal” facilities consitutional. By end of 19th cent. entered period of internationalism marked by development of foreign trade, participation in foreign wars, and acquisition of outlying territories, incl. Alaska, Midway Is., Hawaiian Is., Philippines, Puerto Rico, Guam, Wake I., American Samoa, Panama Canal Zone, and Virgin Is. of the U.S. (qq.v.). Participated in WWI 1917–18; granted suffrage to women 1920 and citizenship to American Indians 1924; suffered Great Depression 1929 ff.; entered WWII after Japanese invasion of Pearl Harbor Dec. 7, 1941; exploded first atomic bomb over Hiroshima, Japan, Aug. 1945, bringing about end of war; founding member of the UN 1945; granted independence to Philippines 1946; provided economic and military assistance to many European nations 1947 ff. under Truman Doctrine and Marshall Plan; founding member of NATO 1949; participated in Korean War (1950–53), U.S. troops constituting major component of UN forces; exploded first thermonuclear device 1952 and granted autonomous commonwealth status to Puerto Rico; declared racial segregation in public schools unconstitutional 1954; intervened militarily in Lebanon 1958; made Alaska and Hawaii states 1959; signed Nuclear Test-Ban Treaty 1963; President John F. Kennedy assassinated Nov. 22, 1963; passed Civil Rights Act of 1964; authorized full-scale intervention in Vietnam War 1964 (see History at vietnam); sent forces to Dominican Republic 1965; mid- to late 1960s marked by widespread civil disorders, incl. race riots and antiwar demonstrations; accomplished first manned lunar landing 1969; invaded Cambodia 1970; returned S Ryukyu Is. (occupied 1945) to Japan 1972; agreed to withdraw all U.S. forces from Vietnam Jan. 1973; sponsored peace negotiations bet. Egypt and Israel 1978–79 through mediation of President James E. Carter, Jr.; abolished Panama Canal Zone 1979; U.S. embassy in Tehran seized by Islamic militants Nov. 1979, its occupants held hostage until Jan. 1981; led coalition forces against Iraq in Persian Gulf War 1991; sent troops to Somalia 1992 to aid starving population; participated in NATO air strikes against Bosnian Serb forces in former Yugoslavia 1995.