I'm just a student of history and not a teacher but I was under the impression that the only verified case of intentional disease spreading was done by the english before the US existed as a separate entity. I'm very curious what historical data you would be referring to. Claims of "stealing" land from native Americans is also, from a historical perspective, misleading. Indians constantly fought over territory and "stole" land themselves. Indians also had a funny way of breaking treaties themselves.
I'm not suggesting that the US is or was always in the right concerning the indigenous peoples but we treated them better then they treated themselves. I also resent that they claim the term "native American". I was born here so I'm a "Native American" too. Of course all of this is beside the main topic.
During the Indian wars some of our more enterprising generals offered various tribes blankets (thru third parties) which had been used to wrap the bodies of smallpox and typhus victims. Wiped out whole villiages this way.
We told them they could live on "X" spot and later found out that it was a great place to lay track for a railroad and then forced them to move to the very inhospitable Oklahoma territories where survival was problematic. Ever hear of something called The Trail of Tears?
Treating them better than the way they treated themselves? That depends on how you define "better," I guess. They treated folks from different tribes in a warriorlike manner, meaning they went to war and if they won, the other tribe was enslaved. That's not just an indian thing, it's a mankind thing. We took away their land (the good stuff) we took away many of their customs like hunting of buffalo (mostly 'cause the hide hunters durn near wiped the species off the planet)....we basically castrated their culture. Hey that's progress. The dominance of the white man was inevitable. Sorry thats just the way it is, but let's not sugarcoat things, either. And sure, the Indians were at times known for going off the reservation a-raiding and a-pillaging. Nobodys hands are clean here.