The War of the Ring was a fierce war which spanned most of the Third Age. It was fought over the One Ring, Sauron's primary source of power. It was also the final battle against the dark forces of Mordor and their lord, Sauron.
The War of the Ring resulted in the defeat of the Dark Lord Sauron once and for all, the destruction of the One Ring and the ascension of Aragorn as the King of Gondor.