I was reading a thing about how in the 1800s the US military went out to kill large numbers of American Bison populations as a way to drive Indians off their lands (through starvation).
That sounds like something Stalin would have done. I'd imagine that there are other, similar instances too.
Is this an act of genocide? An eye of the beholder question? Something else?
To my eye the answer is yes but it is hard to truly pin down a definition for genocide but as you note the US certainly committed acts very similar to Holodomor.
The American Indian Genocide Museum (which I truly recommend to anyone who passes near Houston) takes a very apparent stance and argues forced relocations like the Potawatomi Trail of Death and Choctaw Trail of Tears (which killed 15-20% of the tribe) the smallpox infected blankets given to tribes (some of which they have on display) and the capture, intentional infection and release of tribe members constitutes genocide.
Edit: Smallpox blankets were not used by the United States, capture, infection and release were. Thanks to Gama_Rex for correction.