The ancestors of modern Native Americans arrived in what is now the United States at least 15,000 years ago, possibly much earlier, from Asia via Beringia. A vast variety of peoples, societies and cultures subsequently developed. Native Americans were greatly affected by the European colonization of the Americas, which began in 1492, and their population declined precipitously mainly due to introduced diseases as well as warfare, territorial confiscation and slavery. After the founding of the United States, many Native American peoples were subjected to warfare, removals and one-sided treaties, and they continued to suffer from discriminatory government policies into the 20th century. Since the 1960s, Native American self-determination movements have resulted in changes to the lives of Native Americans, though there are still many contemporary issues faced by Native Americans. Today, there are over five million Native Americans in the United States, 78% of whom live outside reservations.