Are these three sentences worded correctly?

Following Ysval’s demise, one of the surviving Thayan spellcasters dispelled the unnatural darkness enveloping the fortress. The purifying sunlight caused the wraiths and many of the other spectral undead to either perish or disappear, and also provided Nymia and Milsantos’s legions with a significant advantage over the remaining creatures. The Thayan forces soon destroyed all the undead entities and reclaimed the Keep of Thazar.