Complex sentence: Bossuet's own "Discours sur l'histoire universelle" might have furnished an answer, for there the fall of many empires is detailed; but then the "Discours" was composed under a single preoccupation.
Split into simpler sentences: Bossuet's own "Discours sur l'histoire universelle" might have furnished an answer, for there the fall of many empires is detailed. But then the "Discours" was composed under a single preoccupation.