If the American Army understood one thing about the Plains Indians, it was their dependence on the buffalo. Physically and spiritually, the buffalo sustained Sioux tribes. The supply seemed endless. By the first half of the 19th century, there were millions upon millions of buffalo roaming the Plains. The herds were so massive that observers often remarked they had seen a dark solid mass of buffalo as far as the eye could see.

By the mid-1880s the U.S. government was determined to drive all native peoples onto reservations and open up the west for U.S. expansion and settlement. Military attacks on tribal encampments had been going on for years, but the Plains Indians were not easily defeated in battle. It became clear that as long as millions of buffalo roamed the Plains, the U.S. government would not be able to control the warrior tribes of the west. The government needed no official documents to outline its national policy: exterminate the buffalo.

Authorities organized a secret army of hide hunters who succeeded in killing a large number of buffalo in a remarkably short period of time. The U.S. military offered incentives and ensured a safe haven for the hunters along the railways. The herds depleted, fewer and fewer buffalo moved across the land. And while the Canadian government had no overt policy to destroy the animals, herds of buffalo disappeared from the Canadian Plains as well. The war to exterminate the buffalo had been no contest. By early 1883, the animal was all but extinct.

With the buffalo gone, the tribes that had not yet surrendered had no choice but to go to reservations or starve to death. Those who had fled to Canada, including Sitting Bull and his followers, were eventually forced to surrender to U.S. agencies and sent on to reservations.