Conversation so far:
what is warfare?
Three factors led to a growing importance of warfare in Plains Indian culture.
what was the first factor?
First, was the Spanish colonization of New Mexico which stimulated raids and counter-raids by Spaniards and Indians for goods and slaves.
what was the second factor?
Second, was the contact of the Indians with French fur traders which increased rivalry among Indian tribes to control trade and trade routes.
what was the third factor?
Third, was the acquisition of the horse and the greater mobility it afforded the Plains Indians.
did the plains indians get horses?
The Plains Indians raided each other, the Spanish colonies, and, increasingly, the encroaching frontier of the Anglos for horses.
Are there any other interesting aspects about this article?
Although they could be tenacious in defense, Plains Indians warriors took the offensive mostly for material gain and individual prestige.

Question: what was their greatest accomplishment?
Self-contained rewrite: what was the Plains Indians greatest accomplishment?