The exact route and timing of human migration to the Americas are still subject to ongoing research and debate among archaeologists, geneticists, and anthropologists. However, the prevailing theory is that the first humans to reach the Americas arrived via a land bridge that connected present-day Siberia and Alaska during the last ice age, around 15,000 to 20,000 years ago.
This land bridge, known as Beringia, was exposed as a result of lower sea levels caused by the extensive glaciation of the Northern Hemisphere during this time period. It is thought that small groups of humans from Asia crossed this land bridge into the Americas, and then gradually spread southward into different regions of North, Central, and South America over the course of thousands of years.
The evidence for this theory comes from a combination of archaeological, genetic, and linguistic data. Archaeological sites in North and South America contain artifacts that suggest a human presence in the Americas dating back to at least 15,000 years ago, while genetic studies have identified shared ancestry between Native American populations and populations from Siberia and other parts of East Asia. Linguistic studies have also revealed similarities between indigenous languages in the Americas and languages spoken in Siberia.
While there is still much to be learned about the specifics of how and when humans first reached the Americas, the prevailing theory is that this migration occurred via the Beringia land bridge.