The "iron horse," the Indian name for the railroad, was a major factor in
the destruction of the traditional way of life for the Plains Indians. 
The government seized Indian land for the railroad and allowed railroad
tracks to crisscross the buffalo path s.  Troops were transported by rail
to quell Indian disturbances as well as carry framers, ranchers, and
settlers who infringed on Indian land.  The railroad also brought the
sportsmen and hunters who destroyed the buffalo.  Of the approximately
fifteen million buffalo in 1865, only a few thousand remained by the
mid-1880s.  Without the buffalo, the Plains Indian could barely exits. 
The painting above, titled Held up, depicts a train stopped by buffalo.