Reasons for Asian, European and African residents to immigrate to the United States (please tell them separately)

Early days: Europeans opened up new routes. A large number of Europeans went to America to look for gold, open up manors and slaughter Indians, which led to a shortage of labor, so slaves were transported from Africa to America by triangular shipping routes. Later, the slave trade was banned, and they had to transport workers from densely populated Asia to America to fill the labor gap.

Later period: American economic law exhibition is rapid, and a large number of people go to the United States to look for business opportunities.