The Sioux were notorious for wiping out smaller tribes, genocide was a fun hobby for them. Even after reservations came along, they still bullied the smaller tribes, like the Osage, who traded some good land for a smaller parcel of crappy land in the hopes they would be left alone if they didn't have anything the other indians wanted to steal; the crappy land turned out to be the best oil lands in OK., and they became the richest tribe per capita in the country. Serendipity at work.