What is a reservation, who lived there, and why?

An Indian reservation is a legal designation for an area of land managed by a Native American tribe under the US Bureau of Indian Affairs, rather than the state governments of the United States in which they are physically located.The passage of the Indian Removal Act of 1830 marked the systematization of a US federal government policy of forcibly moving Native populations away from European-populated areas.

One example was the Five Civilized Tribes, who were removed from their native lands in the southern United States and moved to modern-day Oklahoma, in a mass migration that came to be known as the Trail of Tears. Some of the lands these tribes were given to inhabit following the removals eventually became Indian Reservations.

In 1851, the United States Congress passed the Indian Appropriations Act which authorized the creation of Indian reservations in modern-day Oklahoma. Relations between settlers and natives had grown increasingly worse as the settlers encroached on territory and natural resources in the West.

If he breaks the law then he had to resign from his post and so he'll lose his/her powers.