Complex sentence: The true corruption of art, however, began after the Crusades, when the abuse of papal power was rampant, and the rich-perceiving contradictions between the actions of the Church and the message of Christianity-began to doubt.
Split into simpler sentences: The true corruption of art, however, began after the Crusades, when the abuse of papal power was manifest. The rich-perceiving contradictions between the actions of the Church and the message of Christianity-began to doubt.