Why did the Lakota Cheyenne and Arapaho tribes fight American military forces?

The Lakota, Cheyenne, and Arapaho tribes fought American military forces primarily to defend their lands, resources, and way of life against encroachment by settlers and the U.S. government. The discovery of gold in the Black Hills and subsequent westward expansion led to increased tensions, broken treaties, and military confrontations. These tribes sought to resist displacement and protect their sovereignty, culminating in notable conflicts such as the Battle of Little Bighorn. Their resistance was rooted in a desire to preserve their cultural identity and autonomy amid growing American colonial pressures.