Much later, Jenseny is going to have a vision of the young knight who first carried Damien's Fire. And as I remember, he is a member of Damien's Order. So that was the Crusade against the Forest.

That also seems to be when Damien's Order died out in the east--and what killed them all.

(That young man tells Jenseny, "Some things are worth dying for" and it wasn't until this reread that I realized how much he paralleled Damien.)