▁buff alo ▁and ▁the ▁Pla ins ▁Indian ▁were ▁virt ually ▁in separ able ." ▁ ▁Native ▁American ▁invol vement ▁According ▁to ▁historian ▁P ek ka ▁H äm äl ä inen , ▁a ▁few ▁Native ▁American ▁tribes ▁also ▁partly ▁contributed ▁to ▁the ▁collapse ▁of ▁the ▁b ison ▁in ▁the ▁southern ▁Pla ins . ▁By ▁the ▁ 1 8 3 0 s ▁the ▁Com anche ▁and ▁their ▁al lies ▁on ▁the ▁southern ▁pla ins ▁were ▁killing ▁about ▁ 2 8 0 , 0 0 0 ▁b ison ▁a ▁year , ▁which ▁was ▁near ▁the ▁limit ▁of ▁sust ain ability ▁for ▁that ▁region . ▁Fire ar ms ▁and ▁horses , ▁along ▁with ▁a ▁growing ▁export ▁market ▁for ▁buff alo ▁ro bes ▁and ▁b ison ▁meat ▁had ▁resulted ▁in ▁larger ▁and ▁larger ▁numbers ▁of ▁b ison ▁killed ▁each ▁year . ▁A ▁long ▁and ▁inten se ▁dr ought ▁hit ▁the ▁southern ▁pla ins ▁in ▁ 1 8 4 5 , ▁last ing ▁into ▁the ▁ 1 8 6 0 s , ▁which ▁caused ▁a ▁w ides p read ▁collapse ▁of ▁the ▁b ison ▁her ds . ▁In ▁the ▁ 1 8 6 0 s , ▁the ▁ra ins ▁returned ▁and ▁the ▁b ison ▁her ds ▁recovered ▁to ▁a ▁degree . ▁ ▁Rail road ▁invol vement ▁After ▁the ▁Pacific ▁Railway ▁Act ▁of ▁ 1 8 6 2 , ▁the ▁west ▁experienced ▁a ▁large ▁bo om ▁in ▁colon ist ▁population — and ▁a ▁large ▁decl ine ▁in ▁b ison ▁population . ▁As ▁rail ways ▁expanded , ▁military ▁troops ▁and ▁supplies