Final answer:
The last group to cross the Beringia land bridge were the Paleo-Indians about 14,000 years ago, whose migrations led to the diverse cultures in the Americas. They followed megafauna across the land bridge during the last glacial period and eventually developed agricultural societies.
Step-by-step explanation:
The last group of people to cross the Beringia land bridge were the Paleo-Indians. During the last glacial period, around 18,000 years ago, these hunter-gatherers traversed Beringia from Siberia into Alaska, following large game like mammoth and mastodon, and later spreading throughout North and South America. As the ice age ended and glacial ice retreated, they migrated in waves into the continental United States and beyond, creating a diverse array of cultures and societies.
Scientific and archaeological evidence strongly supports the Bering Land Bridge hypothesis, suggesting that continuous migrations occurred between about 14,000 years ago and this period marked the arrival of the ancestors of the Native Americans into the Western hemisphere. Over time, the environmental changes led to the end of the Paleo-Indian era, with subsequent cultures developing agriculture, particularly the cultivation of staples such as corn, beans, and squash.