Per Wikipedia:

"The Sun Dance is a ceremony practiced by some Indigenous people of United States of America and Canada, primarily those of the Plains cultures. It usually involves the community gathering together to pray for healing. Individuals make personal sacrifices on behalf of the community.

After European colonization of the Americas, and with the formation of the Canadian and United States governments, both countries passed laws intended to suppress Indigenous cultures and force assimilation to majority-European culture. They banned Indigenous ceremonies.

The Sun Dance was one of the prohibited ceremonies.

Canada lifted its prohibition against the practice of the full ceremony in 1951.

But in the US, Indigenous peoples were not allowed to openly practice the Sun Dance or other sacred ceremonies until the late 1970s, after they gained renewed sovereignty and civil rights following a period of high activism.

The US Congress passed the American Indian Religious Freedom Act (AIRFA) in 1978, which was enacted to protect basic civil liberties, and to protect and preserve the traditional religious rights and cultural practices of American Indians, Eskimos, Aleuts, and Native Hawaiians.

Several features are common to the ceremonies held by Sun Dance cultures.

These include dances and songs passed down through many generations, the use of a traditional drum, a sacred fire, praying with a ceremonial pipe, fasting from food and water before participating in the dance, and, in some cases, the ceremonial piercing of skin and a trial of physical endurance.

Typically, the Sun Dance is a grueling ordeal for the dancers, a physical and spiritual test that they offer in sacrifice for their people. According to the Oklahoma Historical Society, young men dance around a pole to which they are fastened by 'rawhide thongs pegged through the skin of their chests'.

While not all Sun Dance ceremonies include piercing, the object of the Sun Dance is to offer personal sacrifice for the benefit of one's family and community. The dancers fast for many days, in the open air and whatever weather occurs."