1.1A continent already peopled

Human beings reached the Americas at least 15,000 years ago, and quite possibly earlier, migrating from Asia during the last Ice Age when lower sea levels exposed a land bridge across what is now the Bering Strait. Some groups may also have moved south along the Pacific coast by boat. Over millennia, their descendants spread across two continents and adapted to nearly every environment on Earth—Arctic tundra, eastern woodlands, desert Southwest, Great Plains, and Pacific coast.

By 1492 the Americas held tens of millions of people. Estimates vary widely, but the hemisphere was densely inhabited, not the "empty wilderness" of later myth. These were not a single people but a vast mosaic of societies, as different from one another as the nations of Europe, speaking languages belonging to dozens of unrelated families.