Answer:
The introduction of horses
Explanation:
The horses came as the Spanish first came in contact with the nomads , which hunted bisons as a means of living around the 1700's. The emblematic group perhaps, the Cheyennes, an indigenous groups livinig east to the Great Plains. They often went west to hunt large populations of bisons. When they adopted the use of horse they saw it easier. The hunting with horses , and the warfare forced the Cheyennes to cross west of the Missouri and focus on horseback hunting. This was more profitable than harvesing crops. Specially in North America's arid regions.
They traded bisons meat, using it to prepare robes.
As horsemen were enable to shoot many bison, they then kept the tribe fed, and continued to pursue herds. Not only for food but leather was a product of bisons. Native americans greatly profited from the art of riding horses, to a point where Native Americans moved to souther Plains.
This of course was further broadened with the use of firearms, from Europe
and continued to be a common practice until the 1860's, as some bison populations greatly became endangered.
