Are these three sentences correctly worded?

FYI- Nymia is the governor. After reporting to Nymia, Aoth was promoted to an officer in the Griffon Legion, and he then joined a force that the governor assembled to destroy the undead host, which was advancing down the Pass of Thazar. Nymia’s legions engaged the enemy army at the west end of the pass, but following a brutal battle, the undead creatures defeated the Thayan troops and forced them to retreat. Afterward, the undead horde dispersed into smaller bands in order to ravage the countryside of Pyarados.