Complex sentence: After falling back to Springfield, Missouri, Sturgis handed command of the army over to Sigel, and at a council of war that evening it was agreed that the Union army had to fall back to Rolla, starting at 3 a.m. the next morning.
Split into simpler sentences: After falling back to Springfield, Sturgis handed command of the army over to Sigel. At a council of war that evening, it was agreed that the Union army had to fall back to Rolla, beginning at 3 a.m. the next morning.