The scientific consensus is that all modern human beings trace their "deep" history back to East Africa approximately 200,000 years ago. This "Out of Africa" theory infers from archaeological and other data sources that the ancestors of Aboriginal Australians arrived on that continent approximately 50,000 years ago, Europeans in Europe 40,000-30,000 years ago, East Asians (e.g., Chinese, Japanese, Koreans) in their "recent" ancestral homeland approximately 40,000 years ago, Native Americans in North America (via North Asia) 20,000-15,000 years ago and in South America (via North America) 15,000-12,000 year ago.
Viking explorers and settlers arrived in North America about 1000 years ago, but most of their settlements did not last. Other European explorers, conquistadors, and colonizers began to arrive in North America after Christopher Columbus led a voyage across The Atlantic Ocean in 1492. They continued to colonize North and South America for the next few centuries.
Most black people living in the United States today trace their recent ancestry to West Africa. The first Africans were brought to what is now the United States as indentured servants in 1619. America continued to participate in the trans-Atlantic slave trade until the mid-1800s (i.e., Congress outlawed the trade in 1808, but smugglers illegally continued the practice for several decades after that). During that period, approximately 500,000 enslaved Africans (i.e., about 5% of the number of enslaved Africans brought to the Americas) were brought to what is now the United States.
The following graphics provide estimates of how many people immigrated to the United States and from where they came during various periods of American history.