From 1820 to 1930, the United States received about 60% of the world's immigrants. Population expansion in developed areas of the world, improved methods of transportation, and U.S. desire to populate available space were all factors in this phenomenon. Through the 19th cent., the United States was in the midst of agricultural, then industrial, expansion. The desire for cheap, unskilled labor and the profits to be made importing immigrants fueled the movement. Immigrants were largely responsible for the rapid development of the country, and their high birthrates did much to swell the U.S. population. Often, however, immigrants formed distinct ethnic neighborhoods, tending to remain somewhat isolated from the wider culture. Frequently exploited, some immigrants were accused by organized labor of lowering wages and living standards, though other groups of immigrants rapidly became mainstays of the labor movement. Opposition was early manifested by such organizations as the Know-Nothing movement and in violent anti-Chinese riots on the West Coast.

Restrictions placed on immigration were often based on race or nationality. There were also restrictions against the entrance of diseased persons, paupers, and other undesirables, and laws were passed for the deportation of aliens. The first permanent quota law was passed in 1924; it also provided for a national origins plan to be put into effect in 1929. In 1952, the Immigration and Nationality Act (the McCarran-Walter Act) was passed; while abolishing race as an overall barrier to immigration, it kept particular forms of national bias. The act was amended in 1965, abolishing the national origins quota. Despite overall limits, immigration to the United States has burgeoned since 1965, and the 1980s saw the highest level of new immigrants since the first decade of the 20th cent. In 1986, Congress passed legislation that sought to limit the numbers of undocumented or illegal aliens living in America, imposing stiff fines on employers who hired them and giving legal status to a number of aliens who had already lived in the United States for some time. The Immigration Act of 1990 raised the total quota for immigrants and reorganized the preference system for entrance. The 1996 Illegal Immigration and Reform Responsibility Act led to massive deportations of illegal immigrants. Its provisions were later softened under political and legal attack, but a stricter approach to immigrants in general was adopted by the government following the Sept. 11, 2001, terror attacks.

Canada, in the first third of the 20th cent., began to receive an increasing number of immigrants, attracted by the expansion of agriculture in the west and the development of industry in the east. Australia and New Zealand received many European immigrants in the 19th cent.; the former country has been characterized by a preference for immigrants of British stock and by a policy of excluding Africans and Asians that dated from the late 19th cent. After 1965, however, this policy began to change; by the 1970s Australia had abandoned the system of racial preferences, and Asian immigration rapidly increased. Two major trends in immigration emerged after World War II: Australia and New Zealand became the countries with the highest rates of increase, and large numbers of Europeans immigrated to Africa. In recent decades, immigration to Europe from Asia and Africa has also substantially increased, as has emigration from Eastern Europe to the newly reunified Germany.

See studies by M. R. Davie (1983), I. Glazier and L. DeRosa (1986), V. N. Sinha (1987), D. R. Steiner (1987), and A. Richmond (1988).