What was the most significant affect of the conquest of the west in the latter half of the 19th century? why?

The isolation of Native American tribes and nations to areas labeled "Indian reservations."

I suppose someone else might answer that the conquest of the West was a validation of the idea that expansion throughout the continent was the "Manifest Destiny" of the United States, or that the country's range of resources for industrial progress expanded greatly as a result of movement west.  But for the Native American peoples, the conquest of the West by white settlement meant the loss of their lands and their way of life, and dramatically altered their future.