While the pace of migration had accelerated since the 18th century already (including the involuntary slave trade), it would increase further in the 19th century. Manning distinguishes three major types of migration: labor migration, refugee migrations, and urbanization. Millions of agricultural workers left the countryside and moved to the cities causing unprecedented levels of urbanization. This phenomenon began in Britain in the late 18th century and spread around the world and continues to this day in many areas.
Industrialization encouraged migration wherever it appeared. The increasingly global economy globalized the labor market. The Atlantic slave trade diminished sharply after 1820, which gave rise to self-bound contract labor migration from Europe and Asia to plantations. Overpopulation, open agricultural frontiers, and rising industrial centers attracted voluntary migrants. Moreover, migration was significantly made easier by improved transportation techniques.
Transnational labor migration reached a peak of three million migrants per year in the early twentieth century. Italy, Norway, Ireland and the Quongdong region of China were regions with especially high emigration rates during these years. These large migration flows influenced the process of nation state formation in many ways. Immigration restrictions have been developed, as well as diaspora cultures and myths that reflect the importance of migration to the foundation of certain nations, like the American melting pot. The transnational labor migration fell to a lower level from 1930s to the 1960s and then rebounded.
The United States experienced considerable internal migration related to industrialization, including its African American population. From 1910–1970, approximately 7 million African Americans migrated from the rural Southern United States, where blacks faced both poor economic opportunities and considerable political and social prejudice, to the industrial cities of the Northeast, Midwest and West where relatively well paid jobs were available. This phenomenon came to be known in the United States as its own Great Migration.
The twentieth century experienced also an increase in migratory flows caused by war and politics. Muslims moved from the Balkan to Turkey, while Christians moved the other way, during the collapse of the Ottoman Empire. 400,000 Jews moved to Palestine in the early twentieth century. The Russian Civil War caused some 3 million Russians, Poles and Germans to migrate out of the Soviet Union. World War II and decolonization also caused migrations.