Complex sentence: One year later, Aladdin and Alibaba are reunited during Reim's campaign to conquer Magnostadt and after they help defend the city, the Kou Empire launches a surprise attack.
Split into simpler sentences: One year later, Aladdin and Alibaba are reunited during Reim's campaign to conquer Magnostadt. After having helped defend the city, the Kou Empire launches a surprise attack.