Original sentence: The day is saved when Aragorn arrives with the massive Army of the Dead (see Paths of the Dead) who crush Sauron's forces (this is a condensation: in the books the Dead depart after they defeat the Corsairs and liberate Pelargir, after which Gondor's southern army is now free to rally to Aragorn)
Edited sentence: Fortunately the day is saved when Aragorn arrives with the massive Army of the Dead (see Paths of the Dead) who crush Sauron's forces (this is a condensation: in the books the Dead depart after they defeat the Corsairs and liberate Pelargir, after which Gondor's southern army is now free to rally to Aragorn)