Already confirmed as German king, Henry focused on Sicily, based on Constance's claim to inheritance. In 1194 he went south to conquer Sicily and the Norman kingdom of southern Italy. His goal then became securing the election of his son Frederick II as king of both Germany and Sicily. Though he convinced the German princes to accept him, the Papacy and Italian towns feared an over- powerful sovereign to their north and south. A difficult Sicilian revolt in 1197 was harshly repressed, after which Henry died. His brother Philip of Hohenstaufen then rushed to Germany and acted as Frederick's regent, but the young age of the sovereign encouraged the Welfs, under Otto, to make a play for kingship. Otto was supported by Pope Innocent III. He convinced a group of princes to elect him as king in 1198, so Germany was returned to civil war.
Conflict raged for the next ten years, until Philip was murdered. The pope then crowned Otto emperor, but lost interest in him, and began to favor Frederick II, under his protection. The Pope thought he had extracted a promise from Frederick that once crowned, he would give up Sicily. In 1214, Otto was humiliated along with John of England ant the Battle of Bouvines, so that Frederick could become master of Germany, in addition to Sicily, in whose kingship he had already been confirmed. Innocent died shortly thereafter, so Frederick kept both regions. Like his father, Frederick II (1215-1250) was concerned mostly with Sicily. He had gown up there and was not quite German in character. Through 1220 he saw to the disposition of his northern domains. He basically allowed princes free reign in their domains, continuing his grandfather's policies. Fiefs were made fully hereditary, and princes acquired complete powers of jurisdiction, with the crown even allowing them increased urban authority.
During the 1220s, Frederick II was concerned with out-maneuvering the Papacy. Relations were full of distrust. He had gained Honorius III's support by promising to go on Crusade, yet kept putting it off year after year, blaming the delay on lack of funds, or insufficient manpower or transportation. Honorius was ultimately duped into crowning Frederick Emperor without first requiring him to relinquish Sicily. Gregory IX (1227-1241), however, was a hard-nosed Pope interested in reining in Frederick's snobbery. He excommunicated the Emperor for failing to Crusade, whereupon Frederick did indeed go east. His conduct disappointed the Pope mightily: after tooling around Palestine with his army and avoiding serious hostilities with the Ayyubid Sultan of Egypt, he was able by 1229 to negotiate a conditional return of Jerusalem to Christian control. While Frederick received Jerusalem, Bethlehem, and Nazareth, he allowed Muslims to reside and practice their religion in these areas, and undertook to support no Crusade against the Sultan. Thus, while he was able to obtain Jerusalem for the first time since 1188, his entire crusade, and the Holy City itself, were put under Papal interdict. Gregory IX went on to invade Frederick's Italian lands with a papal army. Frederick defeated it by 1230, then summoned a great council to Melfi, which promulgated a new code of Law for Sicily. Unlike Germany, the king's total authority as legislator and adjudicator was underscored. In the Constitution of Melfi, nobles saw their prerogatives limited, and all major cases were assigned to royal courts. Sicily was administratively divided into provinces, and local officials were supervised by the central government's bureaucrats. To encourage trade, customs duties were decreased. In 1232 Frederick held an imperial assembly at Ravenna, where he proceeded to apply a similar governance system upon the Lombard cities, while the 1232 constitutium in favor princeps conceded even more sovereign rights to German princes.
With a tradition of independent towns, Lombardy resented its new status. As well, Gregory IX harbored much ill will for him. He excommunicated the Emperor, then supported the revival of the Lombard League. The next strong Pope, Innocent IV (1243-1254), went even further. Excommunicating Frederick yet again, he revoked the title of Emperor. It was of little immediate consequence though. German princes had nothing to lose from supporting an absentee king, and the English Henry III was quite weak, and could not gain from continental adventure. Similarly, St. Louis of France was pious but did not favor an imperial papacy. Still, the last decade of Frederick's reign was disappointing. He had to face small revolts in Germany, and combat against the Lombard league was indecisive, with both sides winning as well as losing battles, though German forces fared poorly. By his death in 1250, he had not definitively restored German authority in northern Italy, though Sicily was in his firm control.
If the "Ottonian System" was the abjuration of feudal relations, then a notional "Frederickian System" was the espousal of feudal relations for the sake of something apparently larger--the lasting German dominion in northern and central Italy. Only in Germany would feudal nobles be willing to pay for rights they had usurped anyway. Yet, as realistic and accommodating as the Fredericks were in Germany, they were just as ambitious, and perhaps unrealistic, in Italy. They, as their Saxon and Salian predecessors, have been judged harshly for their descent into Italy. It did, indeed, enervate them on the whole, and it did require them to make compromises with German princes that they may not have had to make otherwise. Of course to say this is to assume that the fursten were not sufficiently powerful on their own to require such policies. Also, to condemn German monarchs for Italian aspirations is to discount the importance in their mind of the Charlemagne ideal of European unity under the Emperor's control. As well, given northern Italy's control of the Alpine passes into southern Germany ands its rebellious duchies such as Swabia and Bavaria, any sensible German monarch would want to be supreme at least in the Milan region. Finally, Italy was this period's most wealthy and industrious area in commercial and urban terms. Tax revenues, customs, and a certain standard of living would be attractive to any leader living to the north. These Italian towns, however, were unique in political technology as well, in a way to make them especially difficult to control.
The initial spur for Italian Towns' growth was the relearning of Ancient Rome's agricultural lessons. 1) They re-terraced the hills; 2) dyked the rivers; and 3) drained the swamps. With the resulting financial surplus towns were able to form. At this stage, in the mid to late 1000s, a new type of government formed, the commune. A sworn association, members pledged to care for each other and terrorize common enemies. They possessed an elected assembly and two consuls as a government. At this stage they went out to surrounding countryside and forced nobles into the towns. Three things permitted this: 1) economically, they survived based on the town-country exchange of wares for food. 2) Independent city-states were only possible in a post-investiture Controversy Northern Italy when German imperial power was at low-ebb; indeed, there was no challenging power until 1158, when Barbarossa came south. Thus, no tradition of control from above existed, and even popes had to tread carefully there. Indeed, it was in the communes that anti-sacerdotalism emerged. 3) Italian nobility never adopted primogeniture, but kept dividing inheritances between the sons, so there were no large domains, and very little power. Also, unlike Northern European nobles, they would often move into towns, unless forcibly brought in. When commune leaders did this, it only increased their powers, allowing alliances between stronger towns, such as Milan, and lesser ones.