Is there a way we can have the Crusades go on forever, and be seen as "morally right" by all Europeans? It need not be against Muslims and it need not be a war of Conquest. Just warfare for the sake of Christendom and on the behalf of the Bishop of Rome.
Would it be possible to pull something like this in a world where the Mongols Invade Europe and subdue it (much like Russia) save for a few enclaves in the south, that manages to launch a protracted centuries-long war of reclamation?