Complex sentence: Commandeering the ships of the Corsairs, Aragorn leads reinforcements up the Anduin to relieve the siege of Minas Tirith, and between them, the forces of Gondor and Rohan defeat Sauron's army in the Battle of the Pelennor Fields.
Split into simpler sentences: Commandeering the ships of the Corsairs, Aragorn leads reinforcements up the Anduin and comes to the aid of Minas Tirith. Between them, the forces of Gondor and Rohan defeat Sauron's army in the Battle of the Pelennor Fields.