What invention ended the way of life for cowboys and plains indians?

Answer: Barbed wire

Barbed wire is often considered to be the invention that redesigned the West. Barbed wire made it possible to fence large areas of land. This meant that cattle could be better restrained, even in large areas. It also meant that cowboys were less needed, as cattle did not need as much supervision as before. Finally, it also changed the way of life of the Plains Indians, as this invention made it impossible for them to migrate and move through large stretches of land, as they had done before.