The campaigns followed the excommunication of Frederick II, Holy Roman Emperor, in 1239 and ended with the death of his grandson Conradin, a claimant to the Kingdom of Sicily.
However, outwardly, the Pope would criticize the emperor for his lack of zeal in re-taking the Holy Land for which Gregory IX excommunicated Frederick II before welcoming him back into the fold with the Treaty of San Germano.
In the Holy Land (1095–1291) Later Crusades (1291–1717) Northern (1147–1410) Against Christians (1204–1588) Popular (1096–1320) On 20 March 1239, Pope Gregory IX excommunicated Frederick II, who was in Padua at the time preparing to campaign against the Lombard League.
[4] The crusade came to Germany in 1241, when Archbishops Conrad of Cologne and Siegfried III of Mainz invaded Hohenstaufen lands in the Wetterau.
A major turning point was the deposition of Frederick II by Pope Innocent IV at the First Council of Lyon in 1245.
[5] Two rival kings were elected in Germany and both pursued the crusade against the Hohenstaufen, Henry Raspe in 1246–1247 and William II of Holland in 1247–1251.
His successor, Conrad IV, left the Holy Roman Empire permanently for Sicily in October 1251.