The minimum time depth by which this migration had taken place is confirmed at circa 12,000 years ago, with the upper bound (or earliest period) remaining a matter of some unresolved contention.The time frame and exact routes are still matters of debate, and the model faces continuous challenges.While these peoples have traditionally remained primarily loyal to their individual tribes, ethnologists have variously sought to group the myriad of tribes into larger entities which reflect common geographic origins, linguistic similarities, and lifestyles.Remnants of a human settlement in Monte Verde, Chile dated to 12,500 years ago (another layer at Monteverde has been tentatively dated to 33,000-35,000 years ago) suggests that southern Chile was settled by peoples who entered the Americas before the peoples associated with the Bering Strait migrations.Chicken pox and measles, though common and rarely life-threatening among Europeans, often proved fatal to the indigenous people, and more dangerous diseases such as smallpox were especially deadly to indigenous populations.
This American agricultural endowment to the world now constitutes more than half of all crops grown worldwide .
The impact of their agricultural endowment to the world is a testament to their time and work in reshaping, taming and cultivating the flora and fauna indigenous to the Americas.
According to the New World migration model, a migration of humans from Eurasia to the Americas took place via Beringia, a land bridge which formerly connected the two continents across what is now the Bering Strait.
Another reason for the dramatic decline of the Native American population were the continuing wars with either Europeans or between feuding indigenous communities.
More recently, collective mobilization among the indigenous peoples in the Americas has required the incorporation of closely-knit local communities into a broader national and international framework of political action.