The Decline of the Plains Indians With the end of Civil war and the beginning of the reconstruction process, America started to expand west. After establishing many cities in the west, the abundance of railroads increased exponentially. This new “Frontier” of America alienated the Plains Indians. After already taking over the Indian’s land, the frontiers’ men started to kill buffalo, the major source of food, clothing and tools for the Indians, for game. To protect their lands and stop the waste of buffalo, Plains Indians had to fight. Although out numbered the Indians decided to fight for their land or die tryi