Complex sentence: Despite the victory, it became apparent that Drummond was not going to move from his defenses, and so Izard withdrew back to Fort Erie where he destroyed the fort and returned to the U.S. side of the river.
Split into simpler sentences: Despite the victory, it became apparent that Drummond was not going to move from his defenses, and so Izard withdrew to Fort Erie. Izard later destroyed Fort Erie and returned to the U.S. side of the river.