According to the Annals of Aman in volume X of The History of Middle-earth, the Valar launched their attack against Melkor in Year of the Trees 1090, and Melkor was defeated in 1099. Converting these dates into conventional years (a somewhat approximate process) the War started a little less than 4,000 years before the first rising of the Sun, and the fighting continued for more than a century before Melkor was finally captured.

This term appears in The Return of the King, where Théoden riding to war is compared to Oromë at the 'battle of the Valar' (V 5, The Ride of the Rohirrim). The lack of capitalisation here suggests that this isn't to be considered an 'official' name for the war.