system
Given the following post, respond as if you're commenting on Reddit:
human
[Lord of the Rings Two Towers] What was the great battle that took place in the bog ?
gpt
During the War of the Last Alliance that brought down Sauron at the end of the Second Age, the forces of Elendil and Gil-Galad met the forces of Sauron before the Black Gate, on what came to be known as the Dagorlad - the Battle Plain. The battle lasted months, but in the end the forces of the Alliance were victorious. Sauron's armies retreated to Barad-dûr, where they were besieged for ~~ten~~ seven years until, at the last of his reserves, Sauron himself came forth, and was destroyed.

The spirits in the Dead Marshes are the unquiet spirits of the dead who fell in that great battle before the Black Gate, where Sauron's armies were broken.