Complex sentence: Honorius'reign was plagued by almost constant barbarian incursions into Gaul, Italy and Hispania, whilst at the same time, a host of usurpers rose up due to the apparent inability of the emperor to see to the empire's defences.
Split into simpler sentences: Honorius'reign was plagued by almost constant barbarian incursions into Gaul, Italy and Hispania. At the same time, a host of usurpers rose up due to the apparent inability of the emperor to see to the empire's defences.