Germany during the Crusades
Frederick II (1215-1250)
His importance
If you want to leave your mark on the world as a ruler, the first thing to do is to live a long time. Frederick managed that, ruling for thirty-five years. He ruled in three distinct kingdoms: Germany, Italy, and Sicily. The nature of the mark he left varied in each because the nature of each kingdom varied. Germany was a kingdom of powerful princes, Italy of powerful cities, and Sicily of a centralized monarchy.
Without trying to draw a conclusion about the legacy of the man, I'll here present a brief description of some of his key actions. If you want to read more about him, there are numerous books.
Germany
Frederick confirmed the princes in their rights and powers in order to gain their support for his ambitions elsewhere. He did this as he was bidding for their support while he was still an eighteen year-old kid trying to claim the imperial throne and he was still doing it decades later. The first important act came at the Diet of Frankfurt in 1220. There he was trying to do two things: to get support for an army, and to get confirmation of the hereditary principle, to maintain the Hohenstaufen dynasty.
To his chagrin, the German princes would not give him all he wanted. They would only recognize his son, Henry, as King, but not that the crown would always remain Hohenstaufen.
Italy
Arguably, Frederick was least successful here, where he most needed it. Germany was to provide men and money, and Germany seemed willing to do so. Italy needed only not to oppose him, but this the northern cities would not do. Chief among his opponents was Milan, but Florence and other cities joined the Lombard League as was convenient.
As a result, all we have for the Kingdom of Italy are a series of military truces, but no legislative works and no great pronouncements, not even on the scale accomplished by the first Frederick. He did manage to keep the Lombard League from overturning imperial authority in north Italy, but that was about all.
Sicily
Frederick asserted his control most thoroughly in Sicily, because Sicily was already a centralized state. The Normans, and especially Roger II, his great-grandfather, had seen to that. Some of that control had slipped away during Frederick's minority, but in 1221 he returned to his homeland. He at once demanded that all titles to all fiefs be returned to the crown for review. He re-granted only a few, in effect overturning the acts of the past twenty years and restoring the authority of the king. By 1223, the Hohenstaufen was in firm control.
Rule over towns and regions in Sicily was accomplished by crown servants, not by feudal lords. When he was in the south, he took a direct interest in the administration of justice and finance, and he stamped the Sicilian court with his own personality. Here is where the rumors started—that he had a harem, that he had Muslim councillors, and so on. It is true that he had all royal edicts issued in three languages and that he had not only Muslim but also Jewish advisors. This was as much a reflection of Sicilian society as it was of the personality of the monarch.
The triumph of Frederick's legislation is the Liber augustalis, often called the Constitutions of Melfi. I won't go into the details of this, but it's a wide-ranging work that thoroughly and in detail circumscribed the powers of the nobility, the episcopacy, and the towns. Most of it was lost in the chaos that followed Frederick's rule, but it's quite a remarkable work. For example, it removed the power to prosecute heretics from the bishops. It proclaimed equality before the law. It banned trial by ordeal. And so on. There's really nothing like it elsewhere in 13th century Europe.
Empire and Papacy
Frederick is often portrayed as indifferent in religious matters or even atheistic. He was nothing of the sort. As a ward of Pope Innocent III he was a good son of the Church, as is evidence by the Golden Bull of Eger, which he issued in 1213. By this statement he agreed to clerical elections of bishops as well as the right of appeal to Rome. This seemed to give the papacy the control it wanted over the German bishops, something it had been battling for ever since the days of Henry IV.
Other Accomplishments
Frederick wrote quite a bit, but little has survived. One that has is a book on falconry, a remarkable little work that served as the main textbook on the subject right down to modern times.
The emperor founded the University of Naples, though at the time it was only called a studium.
His accomplishments in Outremer I cover separately.