A Storm on the Horizon
At the onset of 11A The Crimson King regained the Mantle of the Ebon King from Ishar, the Ebon King. Using the Mantle the Crimson King reasserted control of The Undead Host and began to use them to overrun the whole of Akeroth.
After the destruction of the Beacon of Light in 5A and the overrunning of Garem several Military/Religious organisations took it upon themselves to build forts and keep the Host at bay within the Scar. With the re-emergence of the Crimson King and his reassertion of power over the Undead Host these institutions were incapable of stopping the Host and sent a call forth for all people in Akeroth to help them, and so the Crusades began.
The Crusades acted as a series of Military operations aimed at keeping the Undead Host at bay and in check so that the whole of Akeroth would not be overrun and transformed into a plague-zone. Initially only the Original orders that had been occupying the edges of the zones were there, but when the call to arms was stated many people came from across Akeroth and Kul’Adar to save the world. During the Crusades over 1000 forts were established and every nation, region, and people sent troops to aid in the Crusade.
As forts were established and the Undead battled, countless people died and were risen as Undead perpetuating the cycle of the Crusades for hundreds of years. Ultimately the Crusades would last nearly 500 years, and over the course of these years the faith of the people was lost and the world became destitute.
During the Crusades as an influx of troops entered from across Akeroth, a lack of farmers became a major problem, and by the 150th year of the Crusades a drought took place, which then led to a famine and ultimately led to The Grain Riots.
The Crusades would continue for hundreds of years and only end after 12A, after the Cataclysm that affected Ishtar, and gave rise to the God-King Avar, who swept down from the North and ended the Crusades, defeating the Crimson King and resealing the Mantle back in the Ebon Citadel.