Migrations have occurred throughout history and have played an important part in the peopling of all the areas of the earth. Primitive migrations were usually in search of food, but could also result from physical changes, such as the advance of the continental ice sheets, and invasion by other peoples. The most important migrations in European history were the Gothic invasions (3d-6th cent.; see Germans), the Arab invasions (7th-8th cent.; see Arabs), the westward migration of the Golden Horde of Jenghiz Khan (13th cent.), and the invasions of the Ottoman Turks (14th-16th cent.; see Ottoman Empire; Turks).
From the 17th to the 20th cent. migration involved individuals and families rather than nations or mass groups. The basic motive was economic pressure, as areas of low population density attracted people from high-density areas where economic opportunity was low. The desire for religious and political freedom has also been important, and national policies have played a part. In the largest international migration in history, c.65 million people migrated from Europe to North America and South America between the 17th cent. and World War II, while another 17 million went to Africa and Australia.
Nearly 12 million people, most from Mexico or Asia, migrated to the United States in the 1970s and 80s. Within the United States, migration patterns have traditionally been from east to west. Migration from north to south since the 1960s has resulted in the ascendancy of the Sun Belt, a region extending from Florida to S California. This trend has been supported by the southward migration of many blacks. Government regulation of migration became significant in the 20th cent. (see immigration).
Normal internal migration has been characterized by a population shift from rural to urban areas. In the United States, the portion of the population that lives in urban areas has risen steadily from 30% in 1910 to more than 70% in 1990; in Brazil, the percentage of urban dwellers has risen from 30% to 75% since 1940. Within urban areas, a large population shift from central cities to suburbs has occurred in the last half of the 20th cent. The development of totalitarianism and World War II resulted in a new pattern of forced mass migration within Europe. Over 30 million people were forcibly moved or scattered by the Nazis. In the postwar period c.10 million Germans and persons of German descent were forcibly expelled from Eastern Europe.
Other forced migrations since World War II have included the partitioning of India and Pakistan, which uprooted 18 million, and the establishment of the state of Israel, which created about one million refugees (see refugee). After the fall of Saigon (now Ho Chi Minh City) at the end of the Vietnam War in 1975, more than 600,000 fled Vietnam in the face of political persecution; many fled by boat and became known as the "boat people." In South Africa, under the policies of apartheid, blacks were forced to live in designated "homelands" from 1959 to 1994. The Soviet invasion of Afghanistan in 1979 led to the migration of millions of Afghans to neighboring Pakistan and Iran.
In the 1980s and 90s war and civil strife continued to force massive refugee migration in many parts of the world. In Somalia and Ethiopia, civil war combined with long-term drought have resulted in large migrations of peoples (often from rural to urban areas and to neighboring countries) in an attempt to avoid famine. Hundreds of thousands of Kurdish refugees (see Kurds) have migrated from Iraq to Turkey and Iran in the wake of the civil war that followed the Persian Gulf War in 1991. The disintegration of Yugoslavia in the 1990s caused the dislocation of many peoples, especially Bosniaks, Croats, Serbs in areas other than Serbia, and Kosovars. In Rwanda and Burundi, millions of people, primarily Hutus, fled as ethnic civil war wrenched those nations in the mid-1990s; many of them fled to Zaïre (now Congo), where their presence aggravated civil and international strife.
See A. A. Brown and E. Neuberger, Internal Migration (1977); M. Greenwood, Migration and Economic Growth in the United States (1981); G. J. Lewis, Human Migration (1982); W. Weidlich and G. Haag, ed., Interregional Migration (1988).