War of the Alliance

A shorter name² of the war more commonly called the War of the Last Alliance, in which the Elves of Middle-earth allied with the Exiles of Númenor to confront the danger of Sauron in Mordor.

The War began in II 3429, about a century after the founding of Gondor by Elendil and his sons. Sauron's forces emerged from Mordor and captured Minas Ithil, the stronghold of Isildur on the borders of the Black Land. Isildur was able to escape by sea into the North, and there ask help from his father. In response, Elendil allied himself with Gil-galad, King of the Elves in Middle-earth, and together they built a huge army to march south against Mordor.

The fighting began in earnest in II 3434, five years after the loss of Minas Ithil. This was the Battle of Dagorlad, in which the Alliance engaged with the armies of Mordor on the Battle Plain outside the Black Gate. The battle was vicious and prolonged, but the Alliance won the field and marched on Barad-dûr itself.

Thereafter Sauron's Dark Tower stood against a great siege for seven years. At last Sauron attempted to end the War by offering single combat against the leaders of the Alliance. He fought against Elendil and Gil-galad on the slopes of Mount Doom; the combat was terrible, and both Elendil and Gil-galad were slain, but Sauron was also defeated. Thus Isildur was able to take the One Ring from Sauron's lifeless body, paving the way for the War of the Ring more than three thousand years later.