The discovery of gold in the area where native american indians were living and then non compliance to move to reservations ,the US army was sent to confront them.
Custer was unaware of the number of Indians fighting under the command of Sitting Bull at Little Bighorn, and his forces were outnumbered and quickly overwhelmed in what became known as Custer’s Last Stand.
By the late spring of 1876, more than 10,000 Native Americans had gathered in a camp along the Little Bighorn River which they called the Greasy Grass:in defiance of a U.S. War Department order to return to their reservations or risk being attacked.