Complex sentence: However, an unseen maneuver performed by Velásquez' artillery proved deadly and decimated the Allied left by entire ranks; soon entered into battle, the new Allied battalions were obliterated by a precise and concentric fire, killing about 80% of their men within the hour.
Split into simpler sentences: However, an unseen maneuver performed by Velásquez'artillery proved deadly and decimated the Allied left by entire ranks. Pretty soon, Camacho's advance was obliterated by a precise and concentric fire that killed about 80% of the soldiers within the hour.