Immigration is the voluntary movement of people from one country to another. They usually move with the aim of permanently settling in the adopted country. A closely related term is emigration. It refers to movement out of a country. When people depart their homelands for new homes elsewhere, they are said to be emigrants. Once they arrive in their new countries, they are known as immigrants. Another term, refugees, refers to people who have to flee their homes and go to other countries because they are in serious danger. Often they are victims of war or are being threatened because of their race, religion, or political beliefs.

Immigration is one form of the broader movement of peoples called migration. Migration, or moving from place to place, is as old as humanity itself. In prehistoric times humans lived largely by hunting. Groups of people migrated. They followed the animals on which their existence depended. Even when settled communities based on farming developed, people continued this movement. They experienced growing populations, crop failures, or the pressure of neighboring peoples. So they moved and cultivated new lands.

In more modern times, people have tended to immigrate largely in search of better economic, social, and political opportunities.

Immigration usually involves the crossing of national borders. It is considered a voluntary act, one of personal choice. The forced migration of peoples, such as the African slave trade, is not immigration. Internal migration—the movement of people within a country—is also not a form of immigration. In many countries internal migration takes place as people move from rural areas to cities and from cities to suburbs. Often people travel from one region to another because of economic conditions. Or they may be forced to move because of wars and other conflicts, or as a result of natural disasters.

Forms of immigration existed in ancient times. The Greeks were among the earliest colonists. They founded settlements in Asia Minor, Sicily, and southern Italy at least 2,700 years ago. The Phoenicians were seafarers and traders from what is now Lebanon. They also established themselves in the western Mediterranean region, and elsewhere, at about this time. Their greatest settlement was in North Africa. It was aptly named Carthage, or "new town."

The nature of immigration changed dramatically during the 1400s. That century marked the beginning of the great age of exploration and discovery. Exploration led to the expansion of European power from the Mediterranean region to all of the inhabited continents. European navigators explored new lands in Africa. They discovered new routes to the wealth of Asia. Many of these areas offered opportunities for colonization and trade. But few were suitable for large-scale settlement. The "discovery" by Europeans of the New World of the Americas had the most far-reaching impact on the history of immigration.

Immigration to the Americas followed the epic voyage of discovery, in 1492, by Christopher Columbus. Columbus was an Italian in the employ of Spanish monarchs. Spaniards quickly colonized the islands of the Caribbean Sea. And they settled in what later became Mexico, Central America, and most of South America. The Portuguese founded settlements in what is now Brazil. English, French, Dutch, and smaller Swedish colonies were established in North America. The English colonies were scattered along the Atlantic coast of North America. They eventually evolved into the United States.

The Europeans were not the first immigrants in the Americas, however. Thousands of years earlier, migrating peoples from northeastern Asia had crossed into North America. They came by way of a land bridge (in what is now the Bering Strait), which then linked the two continents. Some of these people continued their migration southward. They passed over the narrow connecting neck of Central America into South America. These earliest-known peoples in the Americas were the ancestors of the Indians. For more information on early American populations, see the articles Colonial Life in America, Exploration and Discovery (Exploring North America; Exploring South America). Also see the articlesIndians, American, Slavery, and Thirteen American Colonies.

The United States has rightly been called a nation of immigrants. In the more than two hundred years of its existence, it has taken in more than 69 million people. They have come from nearly every corner of the world. Many were welcomed by a growing nation. But others were viewed with suspicion and hostility. All contributed something to the United States. Many contributed a great deal.

The first colonists in what would become the United States arrived in the 1600s. Some were adventurers. They sought to make their fortunes quickly in the New World. Others came to escape religious persecution. Or they came to be free to worship as they pleased. Most of the settlers were ordinary people. They undertook the long, dangerous sea voyage, attracted by plentiful land. They hoped to find better economic opportunities. Many of the early colonists were too poor to pay for their passage. They arrived in America as indentured servants. As such, they had to work a fixed number of years for the masters who had paid their way.

The original English settlers were followed by other groups. There were Scotch-Irish, Germans, and smaller numbers of French Huguenots (Protestants), Dutch, Scandinavians, and Swiss. A tiny community of Jews settled in the Dutch colony of New Amsterdam. (New Amsterdam was later renamed New York.) By 1763 the colonial population had grown to about 2.5 million. Of this, about one-third was of non-English origin, including black slaves. Most of the slaves were in the southern colonies.

Immigration slowed considerably during the American Revolution. The Napoleonic wars in Europe also made travel to America difficult. With the restoration of peace in 1815, immigration gradually increased. In 1820 the United States began to keep an accurate record of the number of immigrants arriving each year.

The mid-1800s saw a great new wave of immigration. From 1845 to 1855, nearly 1.5 million Irish immigrants arrived in the United States. They were fleeing poverty and the famine caused by successive failures of their potato crops. During this same period, more than 1 million Germans came to America. They were escaping the upheaval and political repression that followed the unsuccessful 1848 liberal revolution in Europe.

Many of the Irish settled in the Northeast. Most found work as laborers in the growing cities. Or they worked in the region's textile mill towns. The Germans settled mainly in the expanding Midwest. They usually became farmers. Or they worked in such cities as Cincinnati and St. Louis.

Immigration again declined during the U.S. Civil War (1861–65). But it increased once more by 1866. Up until the 1880s, most immigrants to the United States had come from western or northern Europe. Beginning in about 1890, however, a second great wave of immigration began. It came mainly from southern and eastern Europe. More than 3.6 million people arrived between 1891 and 1900. More than half were new immigrants, including Italians, Slavs, Greeks, and eastern European Jews. Religious oppression impelled the Jews to emigrate.

One of the greatest decades of immigration in U.S. history was from 1901 to 1910. Nearly 8.8 million people arrived. Of these, more than 70 percent were from southern and eastern Europe. Another great wave occurred between 1981 and 1990. More than 7.3 million immigrants arrived. Nearly half were from the Americas. More than one-third were from Asia.

Many of the new immigrants arrived at New York City. Between 1892 and 1954 they were received at a U.S. government facility on Ellis Island in New York Harbor. (The facility was closed in 1954 and reopened as a museum in 1990.) Other eastern coastal cities, including Boston, were also first homes of immigrants. Some moved inland. They swelled the populations of cities such as Pittsburgh and Chicago. Others, more adventurous, crossed the country. They settled at places along the way or on the West Coast.

So great was the flow of newcomers during this period that in some U.S. cities immigrants and their children made up the majority of the population. In New York City, people could walk for blocks hearing many foreign languages. They also saw newsstands with many foreign-language newspapers.

Few Asians arrived in the United States until the mid-1800s. They came in response to the growth of California after the discovery of gold in 1848. And they came to build the transcontinental railroad. Japanese first arrived in the United States in the late 1800s and early 1900s. Most of the Japanese, as well as many Chinese, came as contract workers. They worked on farms on the West Coast or on plantations in Hawaii. Filipinos came from what was then the U.S. territory of the Philippines. These years also saw the arrival of emigrants from elsewhere in Asia.

As strangers in a new land, many immigrants faced a difficult period of adjustment. Most tended to settle where people from the same country were already established. Churches and clubs were often gathering places for people of the same ethnic origin. The rapid growth of foreign-language newspapers helped non-English-speaking newcomers to understand American ways. Public schools, in particular, encouraged the children of immigrants to adapt to American life.

The first legislation restricting immigration of an ethnic group was aimed at the Chinese. They were first welcomed as a source of cheap labor. But they later aroused hostility. People in the American West feared their livelihoods were threatened by the lower wages paid to the Chinese. In 1882 the U.S. Congress passed the Chinese Exclusion Act. It suspended new immigration by Chinese workers for ten years. The law was renewed repeatedly before being repealed in 1943.

The second group to be excluded was the Japanese. In 1907 the U.S. government reached a "gentleman's agreement" with Japan. The agreement halted the flow of Japanese workers. It remained in force until 1924. In addition to economic reasons, racial prejudice played a strong role in restricting Chinese and Japanese immigration.

Some Americans wanted drastic curbs on immigration from southern and eastern Europe. They prevailed on Congress to pass legislation requiring a literacy test for newcomers. A law passed in 1917 required immigrants over the age of 16 to be able to read and write at least one language. It failed to restrict southern and eastern European immigration, but later legislation did.

In 1921, Congress passed the Quota Act. It limited yearly immigration from any country to 3 percent of the number of people of that nationality living in the United States in 1910. Three years later, Congress reduced the quota to 2 percent and changed the base year to 1890. This discriminated against southern and eastern Europeans. This was because fewer of them had been in the United States in 1890. The National Origins Act of 1929 changed the base year to 1920 and set an annual total of 150,000 immigrants. It also prohibited immigration from Asia.

After World War II, special laws allowed about 400,000 European refugees to enter the United States. Other laws allowed political refugees to enter during the 1950s and 1960s. Some were fleeing Communism in Eastern Europe. But most were refugees from the Communist regime in Cuba.

Congress had opened the door to refugees. But the quota system remained the basis of U.S. immigration law. Many people wanted the law changed because of its prejudice against certain nationalities. Finally, in 1965, Congress amended the law and abolished the national origins system. It set up a system of preferences for immigration. It gave priority to refugees and people who had special skills. It also favored people who had close relatives in the United States. Ceilings were set for the number of immigrants from the Eastern and Western Hemispheres. In 1978, Congress abolished these separate ceilings in favor of a worldwide total of 290,000 immigrants. Spouses and children of U.S. citizens were excluded from the total. As a result, many more Asians and eastern and southern Europeans emigrated to the United States.

Because the United States has set limits on immigration, many people have sought to enter illegally. People who enter a country without permission from that country's government are called illegal aliens. In the late 1970s the U.S. government reported that it was capturing over 1 million people a year who were attempting to enter the country illegally. In 1986, the U.S. Congress passed the Immigration Reform and Control Act. Its purpose was to reduce the flow of illegal aliens. The law penalized employers who hired illegal aliens. It also offered amnesty (freedom from prosecution) and legal status to those who could prove they entered the country before 1982. In 1990, Congress raised the ceiling for the number of immigrants allowed to enter each year to 675,000, beginning in 1995.

Responding to continuing problems, in 1996, Congress passed the Illegal Immigration Reform and Immigrant Responsibility Act. It raised the money available to the government to catch, detain, and deport illegal aliens.

In 2012, President Barack Obama issued an executive order that changed U.S. immigration policy. It allowed aliens who came to the United States illegally as children to remain in the country if certain requirements were met. If they were successful students and were not criminals, they could have their deportation put off for two years. Illegal aliens who served in the U.S. armed forces who met the same requirements could also stay an extra two years. The president changed U.S. immigration policy again in 2014. He announced that up to 5 million illegal aliens would be allowed to stay in the United States and be given work permits. Most of those allowed to stay would be people who have children who are U.S. citizens. The president issued the new rules in an executive order. He did so after Congress failed to pass a comprehensive immigration bill. Republicans denounced Obama's action.

The newest immigrants to the United States are chiefly Latin Americans and Asians. Many Asian immigrants came in the 1960s and 1970s from Vietnam, Cambodia, and Laos following wars in Southeast Asia. More recently, others have come from China (including Hong Kong and Taiwan), the Philippines, India, and South Korea. Most of the Latin American immigrants have come from Mexico, which accounted for almost 30 percent of all immigrants in 2009. Many other Latin American immigrants came from El Salvador, Guatemala, and other Central American countries. Immigrants have also come from the Caribbean, particularly the Dominican Republic, Jamaica, and Haiti.

According to the U.S. Census Bureau, there were 38.5 million foreign-born people living in the United States in 2009. This amounted to 12.5 percent of the population. Over half were born in Latin America and 28 percent in Asia.

More than half of the foreign-born people lived in just four states—California, New York, Texas, and Florida.

The French and English were the chief European colonizers of what is now Canada. They first arrived in the region in the 1500s and 1600s. They competed for its riches in fish and furs.

Immigration to this vast but lightly populated country was slow. It consisted mainly of British settlers, until the end of the 1800s. Over the next twenty years, increasing numbers of Irish, Germans, Scandinavians, Ukrainians, and Russians arrived. Many helped build the railroads and settle the western plains. After World War II, Canada received refugees from Europe. Several million Canadians also have emigrated to the United States.

Over the last 150 years, people from various European countries have emigrated to South America. These "newer" immigrants have included Germans, French, Italians, British, and Eastern Europeans. Japanese, Chinese, and other Asians also have emigrated to South America. East Indians were originally brought as laborers. They now make up more than half the population of the nation of Guyana. Many South Americans, in turn, have emigrated to the United States, especially in recent years.

Europe has been the site of countless migrations and other large population movements throughout its history. In modern times, the breakup of the Austro-Hungarian Empire after World War I redefined the map of Europe. The dislocation of World War II made refugees of many Europeans. These included Eastern Europeans who fled to the West after the installation of Communist governments in their countries. More recently, some European countries have become concerned about their ability to absorb a growing number of people from Africa, Asia and the Middle East. As a result, some countries, such as the United Kingdom, are looking at ways to limit immigration.

Europeans colonized virtually all of Africa. But they settled in significant numbers in only a few areas. The French established themselves in North Africa, particularly Algeria. British settlers farmed the fertile highlands of Zimbabwe (formerly Rhodesia) and other parts of southern Africa. The most hospitable land for Europeans proved to be what is now the Republic of South Africa. Originally colonized by the Dutch and British, it received immigrants from other European countries as well as from India.

Of all the nations of Asia, Israel stands out as a nation of immigrants. Israel was created in the late 1940s as a homeland for dispossessed Jews. Like the United States, it has received immigrants from almost every corner of the globe.

Chinese and East Indians have emigrated to many areas of the world. They often arrived as contract laborers. Many later became shopkeepers. Some became prosperous merchants. Many ethnic Chinese emigrated to the countries of Southeast Asia. Indians settled in East Africa as well as South Africa.

The first-known inhabitants of Australia were the aborigines. They arrived thousands of years ago, probably from Asia. New Zealand was first settled by the Maori, a Polynesian people.

Colonization by Britain beginning in the late 1700s gave both Australia and New Zealand the English language. Other European immigrants arrived after World War II. Underpopulated Australia has sought new immigrants. It long refused to accept Asians, but this policy was later abandoned.

In the wake of the terrorist attacks on the United States on September 11, 2001, the United States and other countries began tightening their border security. They are concerned that foreign terrorists will enter unnoticed among migrants and travelers. In the United States, an inability to control the flow of illegal aliens across the U.S.-Mexico border has resulted in new policing measures. In 2006, President George W. Bush signed legislation that provides for a 700-mile (1,125-kilometer) security fence to be built along the U.S.- Mexico border to deter incoming illegal aliens.

The number of illegal aliens in the United States declined from 11.8 million in January 2008 to 10.8 million in January 2009. More than 60 percent of the illegal aliens were from Mexico. The decline was attributed primarily to the security fence and other improved policing methods. The economic recession in the United States was another factor. Other reasons for the drop in the number of illegal aliens included the rise in deportations and the decline in Mexican birthrates. In 2012 it was reported that the number of Mexicans immigrating to the United States—legal and illegal—was no longer rising.