 Gregory excommunicated Frederick II on 29 September 1227 , accusing him of breaking his oath to lead a crusade to the Holy Land ; the emperor had dispatched two fleets to Syria , but a plague forced them to return . His wife Isabella died after giving birth to a son , Conrad , in May 1228 . Frederick continued to consider himself king of Jerusalem , in accordance with the precedent set by John during Isabella 's minority . 
 Gregory excommunicated Frederick II on 29 September 1227 , accusing him of breaking his oath to lead a crusade to the Holy Land ; the emperor <a href='been_done' title='1'><mark>had</mark></a> dispatched two fleets to Syria , but a plague forced them to return . His wife Isabella died after giving birth to a son , Conrad , in May 1228 . Frederick continued to consider himself king of Jerusalem , in accordance with the precedent set by John during Isabella <a href='null_genetive' title='2'><mark>'s</mark></a>minority . 
Gregory excommunicated Frederick II on 29 September 1227 , accusing him of breaking his oath to lead a crusade to da Holy Land ; tdaemperor done dispatched 2 fleets to Syria , but a plague forced em to return . His wife Isabella died after giving birth to a son , Conrad , in May 1228 . Frederick continued to consider hisself king of Jerusalem , in accordance with thdarecedent set by John during Isabella  minority .