United States
It is believed that the indigenous peoples of the continental United States, including the natives of Alaska, moved in from Asia. They began arriving twelve or forty thousand years ago, if not earlier. Some, such as the pre-Columbian Mississippian culture in the southeast, developed advanced farming, grand construction, and state-level communities. The native population of America decreased after Europeans arrived, and for different reasons, mostly sicknesses such as smallpox and measles.