It changed their way of life - the way they moved about, the way they hunted, the way war became easier due to their increased mobility, but more importantly the introduction of the horse gave Native Americans a new understanding to breed, raise, and train horses for trade to the "white man". This was something they could control.
Colonial American was eager for more land and began to push westward. The flood of settlers pushing west was led first by "mountain men" - explores who first journeyed west and made contact with the plains Indians. The United States government had begun forcing tribes from the eastern portions of the United States to relocate west of the Mississippi River and later on reservations - designated land given to individual tribes. One of the things Native Americans soon discovered was that the Europeans loved fur and initially these "mountain men", but later entire fur trading companies were willing to trade guns and alcohol for pelts.
Disease introduced to Native Americans had devastated the Indian population. Although diseases such as small pox killed thousands of Native Americans, the introduction of guns and alcohol had a longer lasting, damning effect on the Native American way of life. Changes from past altered their life forever.