A grand concerted effort toward some purportedly worthy cause.
Any of the Papally-endorsed military expeditions undertaken by the Christians of Latin Europe in the 11th to 13th centuries to reconquer the Levant from the Muslims, as well as expeditions along the Baltic Sea and against the Cathars.
Any war instigated and blessed by the Church for alleged religious ends, (especially) papal-sanctioned military campaigns against infidels or heretics.
To make a grand concerted effort toward some purportedly worthy cause.
To go on a military crusade.