Wolves used to roam all over North America. As the population grew wolves and human interactions increased. People began to kill wolves. In 1914 the federal government started funding the elimination of all predators from federal lands. By 1940 almost all the wolves in the lower 48 states were killed.
By 1967 the timber wolf subspecies Canis lupus lycaon, was listed as an endangered species under the Endangered Species Preservation Act of 1966 (32 Federal Register 4001). After the Endangered Species Act of 1973 (ESA) was passed, the Secretary of the Interior also listed the northern rocky Mountain subspecies, C 1. Irremotus, and the Texas subspecies, C. 1. Monstrabilis, as endangered. In 1978 the Secretary designated the Minnesota population of wolves as threatened and all other North American gray wolf populations south of Canada as endangered. .
In 1975, the Fish and Wildlife Service (FWS) assigned the Northern Rocky Mountain Recovery Team to develop an idea to provide for regional recovery and delisting of the gray wolf. Three areas had habitat characteristics appropriate to support wolf populations; northwestern Montana, central Idaho, and Yellowstone National Park were these areas. The Northern Rocky Mountain Wolf Recovery Plan, was approved in 1987. It recommended that each of the recovery areas must me able to maintain a least 10 breeding pairs of wolves for three straight years in order for FWS to think about delisting wolves in these regions. These wolves would produce approximately 300 wolves. The plan also advocated natural recovery. Natural recovery is when the wolf immigrate from Canada. The immigration would happen in Montana and Idaho while reintroduction would be used in Yellowstone. .
The Interior Appropriations Conference Committee set aside $200,000 for the National Park Service (NPS) and FWS to study the wolves. They studied whether the wolves could be controlled within or outside of Yellowstone, how the wolf would affect the grizzly bears in Yellowstone, how the wolf would affect the prey base and big game hunting in the Yellowstone region, and the definition of wolf management zone boundaries.