Why did the U. S. Government continuously break its promises not to occupy or settle Native American lands?

The United States Government was trying to expand westward and profit more and more as the years went on. They knew that they could profit off of native land and due to ideologies such as patriotism, nationalism, and nativism, they were willing to do whatever it took to expand our nation economically and geographically. In addition to this, natives were seen as vulnerable and less than human in the eyes of Americans so they didn’t necessarily believe that taking native land was wrong in its entirety.