The Red River War was caused due to the white buffalo hunters hunting on Indian lands
Step-by-step explanation:
After a new technique of tanning buffalo hides came to prominence, the settlers started looking at the population of buffaloes owned by the plains Indians as the mean to earn more through killing the buffaloes and tanning the hides.
A considerable part of the subsistence of the Indians depended on these buffaloes. The settlers had already started hunting these buffaloes down in order to fetch their hides.
In a matter of a few years, the buffaloes went extinct. This angered the plains Indians and culminated into a war between the settlers and the aboriginals. This war came to be known as the Red River War.