Originally Posted by
Encyclopedia of Arda
The Dagor Dagorath, the great final battle at which the forces of the brothers Manwë and Melkor will face one another, and Arda will be unmade.
Notes
1 Actually, The Silmarillion never specifically states where the Last Battle will take place, though there is one hint. Akallabêth tells us that Ar-Pharazôn and his warriors are imprisoned in the Caves of the Forgotten 'until the Last Battle and the Day of Doom.' The fact that the Caves are located in Aman strongly suggests that the battle would have to take place there. This is apparently confirmed by several references in The History of Middle-earth that place the Last Battle in Valinor itself.