 Complete the following phrase:  In 1455 Carvajal was sent by Pope Callistus III to Hungary to preach a vigorous crusade against the Turks, and for six years was the leader of the first effectual resistance made by Christian Europe to the progress of the Ottoman conquerors of Constantinople 1453. Aided by the Observant Franciscan preacher John Capistran, he gathered an army of about 40,000 men, effected a union with the troops of John Hunyadi, and on 22 July 1456 the 