What do we call the medieval Christian ideal of fighting for faith and protection?

The story behind the answer

It refers to Church-sanctioned warfare undertaken to defend the faith, sacred sites, and Christian communities. From the late 11th century, popes framed certain campaigns as meritorious acts: participants took vows, received penance remissions (indulgences), and fought under papal authority. That distinguishes it from the chivalric code (secular knightly ethics), personal devotion (“knightly piety”), or the institutional identity of military orders (“religious knighthood”).

Rooted in Augustine’s just war thinking, canon lawyers and preachers reshaped the idea into a crusading ideology after Urban II’s call at Clermont (1095). It extended beyond the eastern expeditions to the Iberian Reconquista and Baltic campaigns. The ideal brought spiritual incentives and legal protections, while also transforming European politics and finance through crusade taxation, vows, and mass preaching—an ideology whose lofty aims often collided with the messy realities of medieval warfare.