Complex sentence: Misgovernment and fiscal oppression during the Thirty Years' War aroused much discontent throughout the Kingdom of Naples, which broke out in a revolt at Palermo in May 1647, wherein the people of Naples followed the example of the Sicilians.
Split into simpler sentences: Misgovernment and fiscal oppression during the Thirty Years' War aroused much discontent throughout the Kingdom of Naples. A revolt broke out at Palermo in May 1647, and the people of Naples followed the example of the Sicilians.