Bizon

The American bison (Bison bison), also commonly known as the American buffalo, is a North American species of bison that once roamed the grasslands of North America in massive herds. Their range once roughly comprised a triangle between the Great Bear Lake in Canada's far northwest, south to the Mexican states of Durango and Nuevo León, and east along the western boundary of the Appalachian Mountains. Because of commercial hunting and slaughter in the 19th century, the bison nearly became extinct and is today restricted to a few national parks and reserves. (...)

19th-century bison hunts

Bison were hunted almost to extinction in the late 19th century (...) and were reduced to a few hundred by the mid-1880s. They were hunted for their skins, with the rest of the animal left behind to decay on the ground. After the animals rotted, their bones were collected and shipped back east in large quantities.

A long and intense drought hit the southern plains in 1845, lasting into the 1860s, which caused a widespread collapse of the bison herds. In the 1860s, the rains returned and the bison herds recovered to a degree.

The railroad industry also wanted bison herds culled or eliminated. Herds of bison on tracks could damage locomotives when the trains failed to stop in time. Herds often took shelter in the artificial cuts formed by the grade of the track winding through hills and mountains in harsh winter conditions. As a result, bison herds could delay a train for days. (...)

Dangers

Bison are among the most dangerous animals encountered by visitors to the various U.S. and Canadian national parks, and will attack humans if provoked. They appear slow because of their lethargic movements but can easily outrun humans - bison have been observed running as fast as 35-40 miles per hour (56-64 km/h). Bison are more agile than one might expect, given their size and body structure.

Source: en.wikipedia.org