The reason for the sixth crusade?

The Crusades were popular in Europe in the early Middle Ages. Basically, the Pope was the initiator of such military campaigns. Crusades took place from the 11th to the 13th century. The sixth crusade took place in the years 1228-1229. A distinctive feature of this action was that it was headed not by the Pope, but by the emperor of Rome Frederick 2. He set the goal of freeing Jerusalem from Muslims. This campaign ended with the fact that Catholics and Muslims concluded an agreement, according to which the latter left Jerusalem.