Conversation so far:
Who is Red Cloud?
Red Cloud was one of the most important leaders of the Oglala Lakota.
When was Red Cloud in power of the Oglala Lakota?
Red Cloud was one of the most important leaders of the Oglala Lakota from 1868 to 1909
Who did Red Cloud attack in Red Cloud's War?
Red Cloud as a leader of the Oglala Lakota fought against US forces, attacking their forts in an effort to keep control of the Powder River Country of Montana.
Who supported Red Cloud during his attack in the Powder River Country of Montana ?
In support of him, Sitting Bull led numerous war parties against Fort Berthold, Fort Stevenson, and Fort Buford and their environs.
What did Sitting Bull do to help Red Cloud during attacks in the Powder River Country?
Sitting Bull led war parties against Fort Berthold, Fort Stevenson, and Fort Buford and their environs.

Question: What year was this?
Self-contained rewrite: What year was Sitting Bull's war parties aiding Red Cloud during attacks in Powder River Country?