Last Alliance

The Last Alliance of Men and Elves, also known as the War of the Last Alliance, was the final alliance before the seemingly defeat of Sauron.
In SA 3429, Sauron launched an attack of Gondor. In response to this, Elendil and his ally Gil-galad had enough and went to fight. Durin's Folk also joined them. The leaders met and Amon Sûl  and they camped there for three years while forging weapons.
Elendil's younger son defended Osgiliath as Mordor's hosts attacked. 
The forces later crossed and defeated Sauron's army in the Battle of Dagorlad. The seven year siege marked the fall of Anárion, who was slain in battle. There were three objectives to this war; to unmake the One Ring, to destroy Sauron, and to destroy the foundation of the Dark Tower.
Elendil goes to avenge Gil-galad but a blow from Sauron's mace throws him against some rocks and he is killed. It motivating Isildur to attempt to take up Narsil but the blade was broken. With it, the prince cut off Sauron's finger and destroyed the Dark lord. Elrond, who was young at the time, later led Isildur to Mount Doom, and tried to convince him to destroy the Ring. However, Isildur declined and kept the ring for himself.