What caused a decline in the wolf populations in the United States in the early 1900's?

Natural predators

Human activity

Ice age

Global Warming

The correct answer is human activity.

The Yellowstone national park is one of the natural, which had a high number of wolf population. In late 1800s, the agricultural lands were spread nearby the Yellowstone ranges, the agricultural lands were present in the predation range of the wolf. As the agricultural land was in the predation zone of wolf, the wolves from the forests used to come in the agricultural land and destroy live stock. In order to protect live stock, the local people started killing wolves and even they started poisoning them, which was the major reason for the declination in the number of wolves in early 1900s.