What contradictions in american indian policy did the confrontations between tecumseh's alliance and soldiers and settlers in the old northwest reveal?

The contradiction is is According to the Indian Intercourse Act of 1790, the United States could not simply seize a land owned by indians; United States could only acquire it when the Indians ceded it by treaty.
But during the westward expansion, the soldiers taken the lands by force without getting the treaty from indian representatives.

Awe thanks, do you know anyhting about the reading of Californian Neglected its Duty?