Complex sentence: Following a short siege of the town, the battle was commenced an American effort to encircle and destroy the Spanish garrison at Coamo, Puerto Rico, one of the last Spanish bastions south of San Juan.
Split into simpler sentences: Following a short siege of the town, the battle itself commenced. It was an American effort to encircle and destroy the Spanish garrison at Coamo, Puerto Rico, one of the last Spanish bastions south of San Juan.