Internal or external

Migrations can be described as internal or external. Internal migration is the movement of people within a particular country, and external migration is the movement from one country to another. Historians often focus on external migrations because of their impact on nations and economies. One well-known example is the Atlantic Migration, during which about 40 million people moved from Europe to the Americas in the 19th and 20th centuries. Internal migrations often reveal much about changes in a society. The movement of millions of families from large U.S. cities to suburbs since the 1950s is an example.

Voluntary or forced

Some people migrate voluntarily, which means that they choose to move to another place. Many decide to move for economic reasons, expecting to improve their prospects of finding work. For example, many people moved from rural areas to cities during the Industrial Revolution in the 18th and 19th centuries because there were more jobs in the industrial centers than in the countryside. In Russia in the 19th century, millions of people moved eastward from European Russia (west of the Ural Mountains) to Siberia to claim vast new lands for farming. Some people decide to move to get away from unpleasant or difficult circumstances, including religious and racial problems. They are attracted to a place where there is greater freedom, tolerance, and economic opportunity. The Puritans who sailed to North America in 1620 were fleeing from religious persecution in England.

Other people may not wish to migrate but are forced to do so. Throughout history people have been forcibly removed from their homes, through war, being sold into slavery, or natural disasters such as earthquakes, hurricanes, floods, and famines. One of the most devastating instances of forced migration was the removal of people from their African homes to be sold as slaves and transported to the New World. The African slave trade, practiced from the 16th to the 19th century, brought an estimated 20 million people to North and South America. (See also slavery.)

The transportation of criminals was once a common cause of forced migration. Before the American Revolution in the 18th century, England sent its criminals to the American colonies. Afterward England started to use Australia as a penal colony. More than 150,000 convicts were shipped to Australia between 1788 and 1867. Similarly, Spain and France sent their criminals to their American possessions.

Prehistoric and ancient times

Archaeologists have found evidence that the earliest humans originated in Africa. In a sense, all human life is believed to have emigrated from that continent. It is not known exactly when early humans moved into Europe and Asia, but in one well-known migration of prehistoric times humans first reached North America between 20,000 and 35,000 years ago. At the time Asia was connected with what is now Alaska by a land bridge, which no longer exists. It is believed that Asians who crossed the bridge were the ancestors of the Native Americans. Over thousands of years these people moved south and east across North and South America.

The Old Testament of the Bible records a mass migration of the Hebrews, or Jews, from Egypt in the 13th century BC. The Hebrews were fleeing from slavery to freedom in a new land known as Canaan (Palestine). In the 20th century the country of Israel was created on this land as a homeland for the Jewish people.

In the 4th and 5th centuries AD the Roman Empire declined in power as a result of one of the largest movements of people in history. A number of European tribes invaded the empire as they were pushed westward by the fierce Huns of central Asia. A tribe called the Visigoths attacked Rome in AD 410, and the Roman Empire in the West came to an end in 476.

The Middle Ages

In the Middle Ages people moved away from their homelands as a result of a seemingly endless series of wars and conquests. Armies united by the religion of Islam left the Arabian Peninsula to conquer parts of Africa, Asia, and Europe in the 7th century. The Franks, led by Charlemagne, drove the Saxons out of what is now Germany into Scandinavia. This Saxon migration may have been one cause of the raids by the Scandinavian Vikings, who conquered and settled in parts of Europe from the 9th to the 11th century. The Turks and the Mongols moved westward to conquer much of Asia and eastern Europe.

All of these wars displaced great numbers of people and led to the transfer of whole groups from one location to another. Over a period of several hundred years, these migrations changed the ethnic makeup of Europe and much of Asia. They laid the foundation for the modern nation-states of Europe and Asia.

Migration to the Americas

The European discovery of the Americas in the late 15th century began a new era of migrations. Spain, Portugal, France, England, and the Netherlands sent out explorers and colonists to settle various regions of what was called the New World. However, the number of people who came from Europe to live in the Americas in the 300 years ending in 1800 was not large. The majority of newcomers to the Americas during this time were African slaves. About 10 million of them were brought over before 1800.

In the early 19th century serious problems with farming in Europe began the period known as the Atlantic Migration. European farmers struggled through a series of natural disasters—extreme cold, too much or too little rain, flooding, and crop failures. The old practice of handing down land from generation to generation added to the problems. If the eldest son received the family farm, the younger children had fewer opportunities. If the children divided the farm, the plots were smaller. Either way, the sizes of farms were shrinking, and the New World promised huge tracts of land for growing crops.

The Atlantic Migration was perhaps the greatest movement of people in history. Germans migrated to Illinois, Missouri, and Wisconsin beginning in the 1830s. Norwegians and Swedes arrived in the next few decades in Minnesota, Wisconsin, and the Dakotas. In the 1840s a failure of the potato crop in Ireland led many people to move to the Americas. The Irish settled first in Boston and New York and then moved westward.

World War I and the Russian Revolution caused huge numbers of people to leave their homelands in search of better lives in the Americas and elsewhere in the early 20th century. As these new immigrants competed for jobs, unemployment rose. In response, the United States began setting quotas, or limits to the number of immigrants from specific countries. The first quota law was passed in 1921.

World War II and after

World War II led to what are probably the largest forced migrations in history. The Nazis who led Germany forced 7–8 million people from their homes to work for the German war effort. In the closing year of the war and afterward, the Soviet Union forcibly expelled 9–10 million ethnic Germans from eastern Europe into Germany. In the decades after the war, the Soviet Union also deported many political prisoners (people imprisoned because they disagreed with the government) to Siberia. This practice had been common in Russia since the 18th century.

Major political upheavals in the years just after World War II also brought about huge migrations. When the British colony of India was divided into the independent countries of India and Pakistan in 1947, about 18 million people fled in one direction or another. After Communists took over China in 1949, about 2 million Chinese people left to seek greater freedom in Hong Kong and Taiwan.

The creation of the state of Israel in 1948 led to migrations both to and away from the area. Jews had already been migrating to Palestine for decades as a result of the movement called Zionism, which sought to establish a Jewish state. The official recognition of Israel in 1948 encouraged further migration of Jews to the Middle East from all over the world. At the same time, the Arabs who had been living in Palestine before the creation of Israel were driven from their homes. Many of these people, called Palestinians, spread throughout various countries of the Middle East. Decades of fighting in the Middle East have added to the problem.

War-related forced migrations have continued to be very large. The Korean War, revolutions in Hungary (1956) and Cuba (1959), the Vietnam War, and fighting surrounding the breakup of Yugoslavia in the 1990s were a few of the conflicts that caused massive dislocations. In Afghanistan millions of people left their homes as a result of a series of events—a Soviet invasion in 1979, civil war and harsh rule in the 1990s, and a U.S.-led military campaign in 2001. The Persian Gulf War of 1991 and a U.S.-led invasion in 2003 forced many people to leave Iraq. Many of the people displaced by these conflicts returned home when the fighting ended or were resettled in other countries. Others have remained homeless, living in refugee camps. (See also refugee.)

The United States stopped using quotas that limited immigration from specific countries in 1965. However, it continued to set limits on the overall number of people entering the country. In the last decades of the 20th century many people began to move north from Mexico and other Latin American countries to seek better lives in the United States. At the start of the 21st century Mexico was the leading source of legal immigrants to the United States, followed by the Asian countries of China, India, and the Philippines. Illegal immigration became an issue for the United States as growing numbers of people crossed its borders without following the proper procedures.

The leading trend in internal migration during the 20th century was the movement from rural to urban areas. As a result, cities grew very rapidly in much of the world. This was especially true in developing countries. In the United States, many people also moved from northern cities to places with warmer climates in the South and West.