From a time when there were millions of them roaming across much of the continent to a time when their numbers were reduced to two small herds in all of North America, the American bison went through bad times after the white man came to this part of the world. They were killed for sport, slaughtered. The efforts of the American Bison Society were instrumental in turning around the bison's fortunes. In 1894, the U.S. Department of the Interior prohibited the killing of any more bison in Yellowstone National Park. Slowly, the herds began to grow. The American bison is related to the aurochs of Europe, which also enjoy a protected status in Eastern European reserves.