Why did the conflicts between the U. S. government and indigenous nations lead to the "Trail of Tears?

Working on behalf of white settlers who wanted to grow cotton on the Indians' land, the federal government forced them to leave their homelands and walk thousands of miles to a specially designated "Indian territory" across the Mississippi River. Resulted from the enforcement of the Treaty of New Echota, an agreement signed under the provisions of the Indian Removal Act of 1830, which exchanged Indian land in the East for lands west of the Mississippi River, but which was never accepted by the elected tribal leadership