The country of immigrants, the US became a home to most diverse ethnic groups from the whole world. Yet before the colonization of Americas began, West Norse tribes had reached the land and tried to settle there. They presumably were defeated by the indigenous people who inhabited these lands for thousands of years. As most of North America was once covered with ice, even the very initial native Americans came from another continent. There is an evidence that the first Americans came from Siberia across the Bering Land Bridge that is now submerged in water. They were people of North Asian descent. For thousands of years, they lived in Beringia, right nearby Alaska, and their genetic appearance changed almost completely during that time.
When Columbus discovered the New World, Europeans finally set foot on the North American land. Spain, France, and Portugal were the first to colonize the land. As the settlement continued for centuries, more nations arrived at the present territory of the US. The map of ethnic heritage created by the US Census Bureau in 2000 shows that German ancestry covers the majority of the US territory. Germans first came to the US in the 17th century, and the peak of immigration fell on the 19th century. By the way, we owe Germans for bringing kindergartens, Christmas trees, and hot dogs to the US.
Unsurprisingly, African Americans are the second largest group inhabiting the US territory. The majority of African Americans live in Southern states where their forefathers once were brought to work on the cotton plantations.
Mexicans are another large ethnic group in the US. More than 30 million of Mexican descendants inhabit Southwestern states. Besides Germans, many more Europeans settled in the US over centuries. They are Irish (more than 35 million people) as well as English, Italian, French, Polish people whose ancestors once found freedom on the American land.