Stream now with the PBS app + YouTube. 60 million American bison, commonly known as buffalo, once thundered across the prairies of North America — until 1889, when they were almost driven to extinction. These mighty giants terraformed the land, diversified prairie ecosystems, and sustained many native tribes across the continent. Now, tribes and conservationists join forces to bring the species back from the brink, finally returning the American bison to their native grasslands.