The ancestors of living 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, including biological warfare, territorial confiscation and slavery. After its creation, the United States, as part of its policy of settler colonialism, waged war and perpetrated massacres against many Native American peoples, removed them from their ancestral lands, and subjected them to one-sided treaties and to 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.