The Rev. Ralph Abernathy, right, president of the Southern Christian Leadership Conference, visits with American Indian Movement leader Carter Camp on March 8, 1973, at Wounded Knee, S.D. (uncredited/AP)

Carter Camp, a longtime activist with the American Indian Movement who was a leader in the Wounded Knee occupation in South Dakota, died Dec. 27 in White Eagle, Okla. He was 72.

A sister, Casey Camp-Horinek, said her brother had cancer.

Mr. Camp, a member of the Ponca Tribe of Oklahoma, was a longtime member of the American Indian Movement, organizing more than 30 chapters in his home state of Oklahoma, Camp-Horinek said. The American Indian Movement was founded in the late 1960s to protest the U.S. government’s treatment of Native Americans and demand that the government honor its treaties with Indian tribes.

He had a leading role in the Trail of Broken Treaties in 1972, in which a caravan of Native American activists drove across the country to Washington to protest treaties between tribes and the federal government. They took over the Bureau of Indian Affairs for several days.

The following year, Mr. Carter headed to South Dakota with other movement leaders, including Russell Means and Dennis Banks. There they organized the Wounded Knee uprising, a 71-day siege that included several gun battles with federal officers. Means died in 2012 at age 72.

“He was the only person in (a) leadership position in Wounded Knee who never left Wounded Knee, not to go out and do press junkets, not to go and sit in a hotel for a while,” Camp-Horinek said of her brother. “He was a war leader there. He stayed inside with his warriors.”

While several people in leadership roles went on trial for events that took place at Wounded Knee, Mr. Camp was the only one to serve time. He spent two years in prison in Leavenworth, Kan., for assaulting a postal inspector, a charge that Camp-Horinek disputes.

In recent years, Mr. Camp’s focus turned to the Keystone XL pipeline, which he bitterly opposed. Once completed, the contested pipeline would carry tar sands oil from Canada down the midsection of the country and into Texas.

Though Mr. Camp was notified nearly a year ago that he had only a few months to live because of the cancer that had metastasized into his lungs, kidney and liver, Camp-Horinek said her brother’s strength of spirit allowed him to take part in a sun dance, a sacred religious ceremony, in South Dakota this past summer.

Complete information about survivors could not be confirmed.