Answer:
Wolves are animals who usually eat dead animals, so they clear the forests of dead corpses. When wolves were brought back to the park, they not only killed elk, but also changed their prey's behavior patterns. The herbivores started to avoid areas like valleys and gorges where they could be easily hunted by predators. Deer and elk populations increased substantially, resulting in overgrazing, particularly of willows and other vegetation important to soil and riverbank structure, leaving the landscape vulnerable to erosion. Without wolves, the entire ecosystem of the park suffered.
For a specific type of people, a large group was the nomads.
It could be climate, or trade routes.
The annexation of four northeastern states to the Union cause an increase in trade.
