4th Mendevian crusade
The 4th Mendevian crusade was far and away the largest of the crusades up until that point. The precipitating event for this crusade was a balor lord that lead a demon army out of the Worldwound and damaged one of the wardstones that protected Mendev. With the damaged wardstones magic failing, Crusader Queen Galfrey personally led an army of pious templars to drive the demons back out of Mendevian territory. The crusade raged for 15 years, and was essentially a stalemate, although the wardstone was repaired, leading to a relatively peaceful period post crusade.