Why did the plains Indians resent settlers heading west?

The Plains Indians resented settlers heading west primarily because the influx of settlers encroached on their ancestral lands, disrupting their traditional way of life and access to vital resources like hunting grounds and water. Additionally, the settlers often brought diseases that decimated Native populations and imposed foreign social structures, leading to further cultural disintegration. Conflicts over land ownership and differing views on land use exacerbated tensions, resulting in violent confrontations. Ultimately, the westward expansion represented a direct threat to their sovereignty and existence.