Toran invasion of Ha-khet
Known to most of the world as the "War against the undead" (and to Torans as the "Toran-Cascade War"), and it lasted almost 50 years.
Taking place during the Toran Expansion, this war involved the Empire of Tor and the city of Ha-khet in The Great Cascade. Those in charge of Tor had long felt the rampant necromancy that took place within The Great Cascade was something that must be dealt with, and this was their attempt. It was later recorded as a huge military failure.
This conflict ended when the Toran military leaders determined the city was simply too well-defended to conquer and occupy, given they had to first cross an immense desert before even reaching the city.