Honorius III, who succeeded Innocent, could do no better with Frederick, and Gregory IX (1227) came to the papal throne evidently resolved to settle accounts with this young man at any cost. He excommunicated him. Frederick II was denied all the comforts of religion. In the half-Arab Court of Sicily this produced singularly little discomfort. And also the Pope addressed a public letter to the Emperor reciting his vices (which were indisputable), his heresies, and his general misconduct. To this Frederick replied in a document of diabolical ability. It was addressed to all the princes of Europe, and it made the first clear statement of the issue between the Pope and the princes. He made a shattering attack upon the manifest ambition of the Pope to become the absolute ruler of all Europe. He suggested a union of princes against this usurpation. He directed the attention of the princes specifically to the wealth of the church.
Having fired off this deadly missile Frederick resolved to perform his twelve-year-old promise and go upon a crusade. This was the Sixth Crusade (1228). It was as a crusade, farcical. Frederick II went to Egypt and met and discussed affairs with the Sultan. These two gentlemen, both of sceptical opinions, exchanged congenial views, made a commercial convention to their mutual advantage, and agreed to transfer Jerusalem to Frederick. This indeed was a new sort of crusade, a crusade by private treaty. Here was no blood splashing the conqueror, no “weeping with excess of joy.” As this astonishing crusader was an excommunicated man, he had to be content with a purely secular coronation as King of Jerusalem, taking the crown from the altar with his own hand—for all the clergy were bound to shun him. He then returned to Italy, chased the papal armies which had invaded his dominions back to their own territories, and obliged the Pope to grant him absolution from his excommunication. So a prince might treat the Pope in the thirteenth century, and there was now no storm of popular indignation to avenge him. Those days were past.