Around 1830, European trappers, began the slaughter of buffalo for commercial purposes. This included the hide trade and selling the meat to the passing wagon trains on the emigrant trails. With the advent of the railroad companies providing western states with ties to the eastern seaboard, demand for buffalo, increased exponentially. The trains carved up the plains and even encouraged buffalo hunting from train windows as sport. Cowhide brought a higher price than the skin of bulls, so traders killed female buffalo disproportionately, leading to lower birth rates and smaller herds each year. Hoping to effect cultural hegemony, many Anglo-Americans advocated eradicating the buffalo population completely, to starve Native Americans into submission.
Millions of bison, a shaggy broad-shouldered type of buffalo, once roamed the plains, prairies and mountains of North America. Woven into the fabric of Native American life for millennia, the buffalo was revered and honoured, for its importance in their religion, philosophy, and economy. Yellowstone's buffalo herd is the largest free-ranging herd of wild buffalo left in the United States.
During the winter of 1872-1873, the peak season for hide shipments, one firm reported handling 200,000 hides, more than 1,600 pounds of meat, and $2.5 million worth of bones. Records show that approximately 1,500,000 hides shipped in 1872 and 1873, and more than 160,000 in 1874, a total of more than three million hides sent to market in only three years. In 1897, Lost Park, Colorado, poachers exterminated four buffalo, probably the last free-ranging, unprotected herd in the country. In 1894, an inventory in Yellowstone reported only approximately 20 live buffalo. From a population of around 60 million at the beginning of the 19th century, an estimated 1,000 buffalo survived to see the dawn on the 20th century.
In the winter of 1996-97, Many bison starved to death during the region's unusually harsh winter. As the remaining animals migrated north and west in search of food, they left the boundaries of Yellowstone – and the legal jurisdiction of the Park Service – and entered private land or national forest. There more of them, 1,084, according to Yellowstone officials, were shot outright or sent to slaughter, primarily by Montana agents who feared they would spread brucellosis. Many wild bison as well as elk carry the bacterium, Brucella abortus, that causes brucellosis, a contagious disease that can cause miscarriages in domestic cattle. Brucellosis can be passed to humans in the form of undulant fever through unpasteurized, infected milk. The killing of the bison has outraged conservation, environmental and animal rights groups, which maintained this was the largest slaughter of the wild animals since their near-extinction in the 19th century. An activist splashed Agriculture Secretary with bison entrails in Montana in spring 1997. The Fund for Animals has called for a tourism boycott of the state. And American Indian tribes that revere the animal as sacred considered their death a sacrilege.