World population grows as a result of births and declines as a result of deaths. Net migration is the difference between the number of people entering a geographic area (immigrants) and those leaving (emigrants). Over time, migration contributes more than just the initial number of people moving into an area, because the children and grandchildren born to the immigrant population add several times the original number to the population base. There is also an increase in the number of deaths as a result of in-migration.
Most Americans are immigrants or descendants of immigrants who arrived here over the past 200 years. Only a small fraction of the population is related to the American Indians who were here when the first European settlers arrived in the 1600s.
Australia and Brazil are other countries whose current populations consist primarily of descendants of persons who immigrated there during the past two centuries.
In absolute numbers, international migration is at an all-time high. About 145 million people lived outside their native countries in the mid-1990s, and that number increased to roughly 175 million in 2005. Currently, the largest immigration flows are from Latin America and Asia into North America, and from Eastern Europe, the countries of the former Soviet Union, and North Africa into Northern and Western Europe. The Middle East draws migrants from Africa and Asia and hosts millions of refugees from within the region. There is considerable migration within Asia, Africa, and Latin America.
Why People Move
Most people move for economic reasons, but some migrate to escape political or religious persecution or simply to fulfill a personal dream. Some experts divide the many reasons people leave their homes for a new one into push and pull factors. Push factors might be widespread unemployment, lack of farmland, famine, or war at home. The Great Depression (1929–1939) is a good example of a push factor, as hard times encouraged more residents to leave the United States than move in. In the 1980s and 1990s, hundreds of thousands of Africans were pushed out of their homelands to neighboring countries because of famine and civil war.
Factors that attract migrants are called pull factors. These include a booming economy, favorable immigration laws, or free agricultural land in the area to which the migrant is moving. For example, the labor shortage in Japan is pulling record numbers of legal and illegal immigrants to fill the low-status, low-paying, or dangerous jobs that Japanese natives reject. In order to keep a working population that can support its elderly, Japan would need 17 million new immigrants by 2050, according to a recent United Nations report. Other estimates have said Japan would need 400,000 new immigrants each year; however the idea of increased immigration is not favorable to most Japanese.
The majority of migrants to the United States in the past 200 years were European. During the first decade of this century nearly 9 million immigrants entered this country, and more than 90 percent were from Europe (see chart, "Regional Origins of Immigrants to the United States, Selected Years"). By mid-century, just half of the migrants were from Europe. The total number of immigrants fell to around 1 million in the 1940s. In the 1980s the number of migrants increased to levels similar to those at the turn of the century. But 84 percent of these migrants were from Latin America and Asia, and just 10 percent were from Europe. The volume of legal immigration and the prevalence of migrants from Asia and Latin America will continue in the new century.
Percentage of U.S. Population Growth From Migration, 1900–2008
Source: U.S. Census Bureau.
The origins of immigrants change over time, as do their numbers and the effect that they have on U.S. population growth. According to one estimate, about 42 percent of the U.S. population in 1900 resulted from immigration during the preceding century. Immigration was an even greater factor in growth between 1900 and 1950, when 20 million people entered the country. Natural increase added an average of 1 percent of the population increase per year during that period. At that rate the population would have doubled in about 70 years, but it took only 50 years to double. Migration stepped up the doubling by 20 years (see figure, "Percentage of U.S. Population Growth from Migration"). Many immigrants have children once they arrive in the United States, creating further momentum for population growth. Currently, fertility rates of immigrants are higher than those of the U.S.-born population.
The volume of legal migration has fluctuated since the 1930s. Immigration has accounted for an increasing portion of population growth as American women began having fewer children. If current patterns continue, the population of the United States could rise to 438 million in 2050, from 300 million in 2006. According to a recent report by the Pew Research Center, 82 percent of U.S. population growth between 2005 and 2050 will be due to new immigrants and their U.S.-born descendants.
Of the three components of population change, migration is the most difficult component to predict and is most affected by government policies. Because nations can control their borders, they may regulate the flow of legal immigrants. The oil-producing countries in the Middle East offered financial incentives to attract immigrants, just as the United States and Australia once offered free land. In 1990, Japan permitted employment rights and residence for ethnic Japanese from Latin America. The United States' immigrant population (legal and illegal) reached an estimated 37.9 million in 2007. An estimated 12 million were unauthorized.
Emigration: The process of leaving one country to take up permanent or semipermanent residence in another.
Immigration: The process of entering one country from another to take up permanent or semipermanent residence
Net migration: The net effect of immigration and emigration on an area's population in a given time period, expressed as an increase or decrease.
Push-pull factors: A migration theory that suggests that circumstances at the place of origin (such as poverty and unemployment) repel or push people out of that place to other places that exert a positive attraction or pull (such as a high standard of living or job opportunities).
Rate of natural increase: The rate at which a population is increasing (or decreasing) in a given year due to a surplus (or deficit) of births over deaths, expressed as a percentage of the base population.