Conversation so far:
Who began The Great Sioux War of 1876?
By the early 19th century, the Northern Cheyenne became the first to wage tribal-level warfare.
Who was Sitting Bull?
Sitting Bull in Standard Lakota orthography, also nicknamed Húŋkešni  or Slow) was a Hunkpapa Lakota leader who led his people during years of resistance to United States government policies.

Question: What did they do?
Self-contained rewrite: What did Sitting Bull's band of Hunkpapa do preceding The Great Sioux War of 1876?