Complex sentence: The Black Death devastated the region in 1348 causing many monks to die and others to flee the abbey, the decline was compounded during the Hundred Years War when Valmagne suffered attacks and looting by passing mercenaries.
Split into simpler sentences: The Black Death devastated the region in 1348, causing many monks to die and others to flee the abbey. The decline was compounded during the Hundred Years' War when Valmagne suffered attacks and looting by passing mercenaries.