Complex sentence: P. Magdalino, "The Empire of Manuel I Komnenos", 93 Venice, incensed, sent a fleet of 120 ships against Byzantium, which, owing to an epidemic and being pursued by 150 Byzantine ships, was forced to return without great success.
Split into simpler sentences: P. Magdalino, "The Empire of Manuel I Komnenos", 93 Venice, incensed, sent a fleet of 120 ships against Byzantium. Due to an epidemic, and pursued by 150 Byzantine ships, the fleet was forced to return without great success.