The discovery of gold in the Black Hills in 1874 sparked a gold rush that brought thousands of white settlers to the region. The Sioux Indians, who considered the Black Hills their sacred homeland, were angered by the invasion of their territory and the destruction of their hunting grounds. In response, they launched a series of attacks on white settlers and miners.
The completion of the transcontinental railroad in 1869 made it easier for white settlers to travel to the West and for the U.S. military to transport troops and supplies to the region. This made it more difficult for the Plains Indians to resist the U.S. government's efforts to force them onto reservations.
The increasing demand for land by white settlers put pressure on the U.S. government to open up more land for settlement. In order to make land available for white settlers, the U.S. government began to force Plains Indians onto reservations, using military force if necessary.
The change in U.S. policy toward the Plains Indians had a devastating impact on the tribes. In a series of wars and massacres, the Plains Indians were defeated and forced onto reservations. Their way of life was destroyed, and their culture was nearly wiped out.