What were the characteristics of American population migration before World War II?

From the end of 15 to the beginning of 16, the mainstream of population migration was from the "old continent" to the "new continent". The immigrant areas are Asia, Europe and Africa, and the immigrant areas are North and South America, Southeast Asia and Oceania. Among them, the brutal sale of African slaves by European colonists is the largest and longest-lasting forced international migration in human history.

After World War II, the new feature of international population migration is that the proportion of permanent immigrants is declining, and the forms of migration tend to be diversified, which is manifested in the sharp increase of political international population migration.

The flow direction has changed a lot. Europe and the United States have become areas where people move in, and Asia and Latin America have moved out.

The emergence of emerging cities and emerging industries has triggered a large number of population migration.