Complex sentence: Howbert claimed that the account of the battle to the United States Congress made by Lieutenant Col. Samuel F. Tappan was inaccurate, accusing Tappan of giving a false view of the battle because Tappan and Chivington had been military rivals.
Split into simpler sentences: Howbert claimed that the account of the battle to the United States Congress made by Lieutenant Col. Samuel F. Tappan was inaccurate. He accused Tappan of giving a false view of the battle because Tappan and Chivington had been military rivals.