Pagan heresy at that. Think of it like the Northern Crusades, when the Teutonic Knights fought the pagan Baltic tribes in Prussia.
(To be fair, real-life Crusades were messy, controversial, and often cruel endeavors, for example the First Crusade massacred Jewish and Muslim civilians in Jerusalem, but crusader memes are funny, and removing p*rn from Imgflip is a noble cause, so idc, the Imgflip Crusaders are really awesome)