Complex sentence: Sometime in the 1910s, he began telling companions about his experience surviving the Battle of the Little Bighorn, and in 1921, he gave a detailed account of his experiences to a reporter from the "Walla Walla Bulletin".
Split into simpler sentences: Sometime in the 1910s, he began telling companions about his experience surviving the Battle of the Little Bighorn. In 1921, he gave a detailed account of his experiences to a reporter from the "Walla Walla Bulletin".