Complex sentence: The Pontifical States included lands in Avignon and a small enclave to the east ("Comtat Venaissin"), all of which remained part of the Pontifical States up to the French Revolution, during which they became part of France in 1791.
Split into simpler sentences: The Pontifical States included land in Avignon and a small enclave to the east ("Comtat Venaissin"). They remained part of the Pontifical States up to the French Revolution, during which they became part of France in 1791.