Answer:
At first, America was only inhabited by the native American. During the peak of European exploration, many settlers from different part of Europe (Most notably Britain, France, and Spain) Came into America in order to colonize this territory. A lot of them came in while bringing slaves that they kidnap / purchase from Africa.
Centuries after the colony was created, Industrial Revolution started to entered America. This provide a lot of job opportunities In America. Many immigrants from all over the world such as Asia, middle east, Ireland, and Russia came into this country as immigrants. They wanted to work in factories to improve their standard of living. Pver time, this created diverse ethnic groups In America.