After a period of exploration by people from various European countries, Spanish, Dutch, English, French, Swedish, Russian and Portuguese settlements were established. In the 16th century, Europeans brought horses, cats, cattle, and hogs to the Americas and, in turn, took back to Europe maize, turkey, potatoes, tobacco, beans, and squash. The disease environment was very unhealthy for explorers and early settlers.
The pre-Columbian era incorporates all period subdivisions in the history and prehistory of the Americas before the appearance of significant European influences on the American continents, spanning the time of the original settlement in the Upper Paleolithic period to European colonization during the Early Modern period. While technically referring to the era before Christopher Columbus‘ voyages of 1492 to 1504, in practice the term usually includes the history of American indigenous cultures until they were conquered or significantly influenced by Europeans, even if this happened decades or even centuries after Columbus’ initial landing.
It is not definitively known how or when the Native Americans first settled the Americas and the present-day United States. The prevailing theory proposes that people migrated from Eurasia across Beringia, a land bridge that connected Siberia to present-day Alaska, and then spread southward throughout the Americas. This migration may have begun as early as 30,000 years ago and continued through to about 10,000 years ago, when the land bridge became submerged by the rising sea level caused by the ending of the last glacial period.
Conservatism made its comeback in the 1980s under Ronald Reagan. The Cold War ended when the Soviet Union dissolved in 1991, leaving the U.S. the only superpower. The economy was in transition after 1970 from heavy industry (with strong labor unions) to a service economy based on high technology. International conflict returned in 2001 with the September 11 attacks and subsequent War on Terror. By 2008 the worldwide Great Recession opened an era of stagnation or slow growth.
The Soviet Union and the U.S. emerged as opposing superpowers after the war and began the Cold War confronting indirectly in an arms race, the Space Race. U.S. policy was built around containment of the expansion of Communism. American programs to revitalize the economies of Western Europe proved successful in the late 1940s, and NATO was formed as a permanent military alliance with largely American leadership. The Korean War (1950–53) and the Vietnam war (1964–73) were fought to contain Communist expansion.
A political realignment expelled the Republicans from power and installed Democrat Franklin D. Roosevelt and his elaborate and expensive New Deal programs for relief, recovery, and reform. Roosevelt’s Democratic coalition, comprising ethnics in the north, labor unions, big-city machines, intellectuals, and the white South, dominated national politics into the 1960s.