Complex sentence: In 1864, he resigned to tend to his family although historian Ezra J. Warner speculated that he felt, after proving his abilities at Shiloh and Helena, that he was being shelved.
Split into simpler sentences: In 1864, he resigned to tend to his family. Historian Ezra J. Warner speculated that he felt, after proving his abilities at Shiloh and Helena, that he was being shelved.