It could be a combination of both reasons I suppose. The version of events I heard was that the presence of enormous herds made railroad travel impossible, since the rails would be blocked by thousands of grazing animals.
--- On Sun, 9/7/08, John Thornton <jthorn65 at sbcglobal.net> wrote:
> Date: Sunday, September 7, 2008, 9:40 PM
> Yep, you're wrong. More than simply starve however.
> The slaughter of the buffalo was specifically to deprive
> Native
> American's of a primary source of food, clothing,
> housing, etc.
> By killing the buffalo the Govt. felt it could more easily
> control
> nomadic tribes who needed the buffalo to survive.
>