What are the characteristics and problems of population migration in the modern world?

The two world wars blocked the normal international population migration, but as soon as the war ended, the international population migration entered a new historical period and presented some new characteristics. First of all, political international migration has increased dramatically. After the war, Europe redrawed its national boundaries, which made the countries in Eastern Europe enter and leave each other because of the changes in national boundaries. India and Pakistan are divided. It has formed the largest international migration of population in Asia: in independent African countries, the original colonists were forced to repatriate their populations. Second, the flow of international migration has undergone tremendous changes. The demand for labor in the United States has decreased, and a large number of Europeans have returned home from colonies. With the rapid development of European economy and the reduction of population pressure after the war, the number of people who moved out decreased, and the region changed from a place where people moved out to a place where people moved in. Third, the United States is still the main place of immigration, but the source structure of immigrants has changed. European immigration has decreased, and Latin America has become the main source of immigration. After 1970s, the number of immigrants in Asia surpassed that in Europe. After the war, the phenomenon of international population migration changed from capitalist countries to backward colonies to poor countries to rich countries, which had different effects on developed countries and developing China countries.