Editing John of Brienne (section)

== {{anchor|In the Pope's service}}Papal service ==

Honorius did not accept Frederick's unilateral act and continued to regard John as the rightful king of Jerusalem.{{sfn|Perry|2013|p=139}} In an attempt to take advantage of the revived [[Lombard League]] (an alliance of northern Italian towns) against Frederick II, John went to [[Bologna]].{{sfn|Perry|2013|p=140}} According to a version of Ernoul's chronicle, he declined an offer by the Lombard League representatives to elect him [[Kingdom of Italy (Holy Roman Empire)|their king]].{{sfn|Perry|2013|p=140}} Even though this account was fabricated, John remained in Bologna for over six months.{{sfn|Perry|2013|p=141}} The dying Honorius appointed John [[Rector (politics)|rector]] of a [[Patrimony of Saint Peter]] in [[Tuscany]] (part of the [[Papal States]]) on 27 January 1227,{{sfn|Perry|2013|p=142}}{{sfn|Runciman|1989|p=177}} and urged Frederick II to restore him to the throne of the Kingdom of Jerusalem.{{sfn|Perry|2013|p=140}} Honorius' successor, [[Pope Gregory IX|Gregory IX]], confirmed John's position in the Papal States on 5&nbsp;April{{sfn|Perry|2013|p=143}} and ordered the citizens of [[Perugia]] to elect him their ''[[podestà]]''.{{sfn|Perry|2013|p=143}}

Gregory excommunicated Frederick II on 29 September 1227, accusing him of breaking his oath to lead a crusade to the Holy Land;{{sfn|Van Cleve|1969|p=447}} the emperor had dispatched two fleets to Syria, but a plague forced them to return.{{sfn|Van Cleve|1969|p=446}} His wife Isabella died after giving birth to a son, [[Conrad IV of Germany|Conrad]], in May 1228.{{sfn|Perry|2013|p=145}} Frederick continued to consider himself king of Jerusalem, in accordance with the precedent set by John during Isabella's minority.{{sfn|Perry|2013|p=145}}

The imperial army under the command of [[Rainald of Urslingen]] invaded the Papal States in October 1228, beginning the so-called [[War of the Keys]].{{sfn|Perry|2013|pp=145, 147}} Although John defeated the invaders in a series of battles, it took a counter-invasion by another papal army in southern Italy to drive Rainald back to [[Sulmona]].{{sfn|Perry|2013|p=147}} John laid a siege before returning to Perugia in early 1229 to conclude negotiations with envoys of the [[Latin Empire of Constantinople]], who were offering him the imperial crown.{{sfn|Perry|2013|p=147}}