The early thirteenth century saw the intersection of several crusading ventures and European wars. In Greece, a crusade against Christians had produced a new but shaky empire facing external and internal threats, which continued to call, in vain, for support from the West. In 1208 Innocent III launched another crusade against Christians, this time nearer home. The story of the Albigensian Crusade is well known, and still resonates today. A French army under Simon de Montfort headed south, sacking Beziers, massacring its population, occupying Carcassonne and burning heretics. Occitan resistance to Simon de Montfort's army fell apart at the battle of Muret, on 12 September 1213, with the death of Peter II of Aragon. Then three years after proclaiming the Albigensian Crusade, in 1211, Innocent ordered the preaching of a new crusade in Spain, which resulted in the stunning Christian victory over the Moors in July the following year at Las Navas de Tolosa. Meanwhile at the end of 1211 or the beginning of 1212 Frederick II laid claim to the Holy Roman Empire and joined Philip Augustus of France in his war against John of England and the then Holy Roman Emperor, Otto IV of Brunswick. The war culminated in the battle of Bouvines on 27 July 1214, marking the permanent English loss of Brittany and Normandy and Frederick's acquisition of the imperial crown. And five months before the battle of Muret, to launch a new crusade to the Holy Land, the pope issued his great crusade encyclical Quia major, which was to be the main focus of the Lateran council held in 1215. During the second half of April and early May 1213 copies of this supreme example of papal crusade propaganda were issued to almost all the provinces of Latin Christendom. Then at the 1215 council sentence was pronounced on Raymond VI of Toulouse, depriving him definitively of his lands and provisionally sequestering those of the count of Foix.

When Innocent died on 16 July 1216, Honorius III enthusiastically took over his predecessor's programme. From late 1217 crusaders began to arrive in Acre in dribs and drabs, and the army eventually made its way to Damietta, which surrendered to the crusaders in August 1218.