According to Bonacich and Cheng, capitalist development leads to imperialism. As a result, many Chinese and Japanese were displaced from their traditional economic pursuits, becoming available for emigration and they immigrated to the United States. Another reason is as the US developed, its requirements for labor, especially cheap labor, increased.
The issues: Immigrant workers contribute to the development of the country to which they have moved, while their country of origin loses some of its most able-bodied and productive members. Thus based in part on immigrant labor, the developed society becomes increasingly developed, while the poorer societies are likely to remain underdeveloped.
Another issue is that within the receiving country, immigrant workers faced prejudice and discrimination.