Westerners who ruled territories directly denied the influence of natives because they considered the natives to be a threat to their claim to the territory. They believed the territory to be theirs and theirs alone, and having influence of Native Americans in the territory could eventually lead to them claiming the land.
In the early periods of the American West, conflicts between Western people and West bound migrants with Native Americans who inhabited the land were constant. There has been many controversy around this subject, in a story that has as highlights the Indian Removal Act, followed by the Trail of Tears.