Germany during the Crusades
Conrad IV (1250-1254)
Conrad was a young man of twenty-three when his father died, and he had every reason to expect and hope that he would inherit all of his father's vast estates. Indeed, he was in a very strong position, as Frederick had managed to force Pope Innocent to flee to Lyons, where the pope placed himself under the protection of King Louis IX of France. It is not surprising that Conrad therefore inherited papal enmity.
Conrad lived only four more years and spent all four fighting for his life. Innocent excommunicated the man immediately, and in Germany he already had a counter-claimant in William of Holland. When he died unexpectedly in 1254 he had not lost much ground but he had not gained much either.
Conradin (1254-1268)
He did manage to leave a son, also named Conrad, who is formally Conrad V but who is usually called by the diminutive, Conradin. He was still only a child when his father died, and real leadership of the Imperial position in Italy was taken up by Manfred, an illegitimate son of Frederick II.
Manfred
Manfred was as ambitious and effective as his father, and for a time he seemed about to overwhelm papal forces. Then, in 1266, Pope Urban IV offered the crown of Sicily to Charles of Anjou and brother to the French king. Charles was himself a good field commander, and he had an excellent army and ample funds. He was crowned by the pope in January, and by February he forced a battle at Benevento. Not only was Charles victorious, Manfred was killed on the battlefield.
That left Conradin, who was by now a teenager. He was up in Germany. In 1267 a series of revolts in various south Italian towns encouraged him, and in 1268 he led an army over the Alps and into southern Italy. There was a battle at Tagliacozzo, which Charles won decisively. Conradin fled, was captured, held prisoner for a time, then executed in Naples. The "brood of vipers" had been eliminated.