Complex sentence: He next fought at the Battle of Champion Hill, where a counterattack by his division almost split Grant's army in half but the rest of the army failed to support his attack and Bowen was forced to retreat.
Split into simpler sentences: He next fought at the Battle of Champion Hill, where a counterattack by his division almost split Grant's army in half. When the rest of the army failed to support his attack, Bowen was forced to retreat.