Humans migrated to North America about fifteen thousand years ago from Australia.
Europe.
Africa.

Explanation:

Early human migrations are the earliest migrations and expansions of archaic and modern humans across continents and are believed to have begun approximately 2 million years ago with the early expansions of hominins out of Africa of Homo erectus. This initial migration was followed by other archaic humans including H. heidelbergensis, which lived around 500,000 years ago and was the likely ancestor of both Denisovans and Neanderthals. Early hominids were said to have "crossed land bridges that were eventually covered in water" (History Alive, pub. 2004, TCI).