[mrganondorf]

Rereading this part I realized that the state of the Holy War as it emerges from Caraskand and achieves "dark glory" in victory over the Fanim--Bakker is giving us an analogue of what war must have been like in the First Apocalypse.  The Battle at Mengedda was probably similar with the good guys going out to fight and die and then when they happen to win, they can only celebrate as sort of animated cadavers, a sort of wretched rejoicing.

[H]

Indeed, you are probably right, although, I think that what Scott was after was nearly a straight invokation of the actual First Crusade:

In May 1098, Kerbogha of Mosul approached Antioch to relieve the siege. Bohemond bribed an Armenian guard named Firuz to surrender his tower, and in June the crusaders entered the city and killed most of the inhabitants.[92] However, only a few days later the Muslims arrived, laying siege to the former besiegers.[93] According to Raymond D'Aguilers, it was at this point that a monk named Peter Bartholomew claimed to have discovered the Holy Lance in the city, and although some were skeptical, this was seen as a sign that they would be victorious.[90]

On 28 June 1098, the crusaders defeated Kerbogha in a pitched battle outside the city, a victory caused by Kerbogha's inability to organize the different factions in his army.[94] While the crusaders were marching towards the Muslims, the Fatimid section of the army deserted the Turkish contingent, as they feared Kerbogha would become too powerful were he able to defeat the Crusaders. According to Christian eyewitnesses, an army of Christian saints came to the aid of the crusaders during the battle and crippled Kerbogha's army.

All the elements, besiegers becoming the besieged, the sudden "Holy event," the march out and defeating of the new besiegers.  There is the further element of the dispute over the new King and so on.

You can read more here if you are so inclined.