The movement of people from the area of their birth to different parts of the same country, or to different countries has been both the result of uneven development , and a major contributor to population change and rates of development. But migration usually involves young adults, with the result that fertility is reduced in the area of origin and increased at the destination. Also, young migrants often seem willing to work extremely hard to create economic success for themselves and the receiving society.
Migration can be voluntary or forced, temporary or permanent.
Historically, a small number of international migrations have been particularly significant. The earliest of these was the movement of some 10 million Africans to the Americas between the 17th and 19th centuries to provide slave labour to the European colonists. They were vital in producing precious metals and crops, such as sugar and cotton, which boosted European economies and living standards and strengthened mercantile capital. Later, emigration of Europeans, especially to North America, helped to reduce European birth rates and to consolidate European power in many colonies. At the same time there were substantial movements from India and China into Southeast Asia, Africa and North America.