Final answer:
Early humans migrated from Asia to North America across the Bering Land Bridge during the last ice age, later populating both North and South America. This is the most supported theory by genetic and archaeological evidence.
Step-by-step explanation:
Early humans migrated from Asia to North America across a land bridge known as Beringia. This occurred during the last ice age approximately 18,000 years ago when sea levels were lower, exposing the land bridge. The migrants traveled in search of game and in response to climatic conditions and resource availability. This migration event marks one of humanity's profound migratory accomplishments, allowing Homo sapiens to eventually inhabit the Americas.
The journey did not stop there; descendants of these first migrants continued their expansion, covering the entirety of North and eventually South America. This grand migration took place in different waves and by various routes, including coastal and inland paths. With time, these populations established diverse cultures and adapted to a wide range of environments, from the Arctic's frigid landscapes to the tropical climates in the south.
Archaeological evidence suggests that as many as four distinct migrations might have occurred, and genetic research supports the connection between the indigenous peoples of the Americas and ancient Asian populations. While alternative theories exist, the Bering Land Bridge theory remains the most supported by current evidence concerning the peopling of the Americas.