This chapter focuses on scientific evidence from multiple disciplines to answer these questions, focusing in particular on what genetic data have suggested about the population history of the Americas. Genetic drift can lead to deviations from previous generations. The evidence provides an important context for genetic studies investigating the initial peopling of the Americas. In the context of the peopling of the Americas, both single-migration and multiple-migration models have had their proponents. Thus, human migration into the Americas would have been limited both by when Beringia was exposed and by when a route into lower North America was open. Archaeology eventually provided evidence of ancient empires in the Americas as well, including the Mayan, Aztec, and Inca empires. In particular, the archaeological record provides concrete evidence of human settlements in Northwest Asia, Beringia, and the Americas, helping us to determine how long people have been living in each of these areas.