The document provides an overview of the theories surrounding the first peoples arriving in North America. It is widely accepted that during the last ice age, when sea levels were lower, a land bridge connected Asia and North America, allowing people to cross over on foot. As the glaciers melted, the land bridge was submerged again. Archaeological evidence such as tools and traditions have been found that can be traced back to these earliest inhabitants. The document then provides details on the cultures and ways of life of various indigenous groups across North America, including the Iroquoians, Plains peoples, Northwest Coast peoples, and Subarctic peoples.