The balance of power was that although the U.S. Government said that the american indians were sovern nations within their nation, they could still constantly bully them out of land, and stop the spainards and british in canada from supplying them, effectively reducing them to nothing more than a slight deterrant from expanding westward. (look at Johnson V McIntosh)
And for the 1805 treaty, Jefferson gave them the assimilation policy, and Harrison played tricks ,threatend, and bribed tribal leaders to give land, and by 1807, U.S.had extracted from reluctant tribal leaders the treaty rights to eatern Michigan, suthern Indiana, and most of Illinois
