Complex sentence: El Cid was content to let the Almoravid armies and the armies of Alfonso fight without his help, even when there was a chance that the armies of Almoravid might defeat Alfonso and take over all of Alfonso's lands.
Split into simpler sentences: El Cid was content to let the Almoravid armies and the armies of Alfonso fight without his help. Even when there was a chance that the armies of Almoravid might defeat Alfonso and take over all of Alfonso's lands.