If it was actually true to history, then the pony governments would end up enacting laws making it legal to kill the buffalo and destroy their food source. Also, they would give the buffalo all sorts of nasty diseases that would wipe out their population, and force them off their land. Then they would take the buffalo children and send them away to boarding schools, where they'd be abused and required to forget their native languages and convert to whatever religion the ponies follow, essentially destroying their culture.