at the height of their cultures, their main source of food was the large herds of american bison. hunting was not only the main activity of plains indians but was a central part of their religion. their culture was formed from the natural environment they lived in. before horses, it was more difficult for natives to hunt bison. they often had to create traps for the bison. early on, they used bows and arrows, spears, and clubs. later the europeans introduced firearms.