During the 19th century, the United States Government tried to exterminate the bison in order to put the native prairie Indians, who relied massively on the bison, under control. This process was also helped by private farmers who to tried to maximize the amount of fields available for agriculture by killing too many bison.
The bison, however, were also an important ecological factor in keeping the prairies diverse in plants and animals life, and without them, the top layer soil eroded causing the great dust bowl of the 1930s.
Who could have guessed that fucking with the ecosystem isn't a smart idea...