The Byzantine Empire had been destroyed during the Fourth Crusade in 1204, when Frederick was only 9 years old. Frederick’s lifetime coincided almost exactly with the period of the Latin Empire of Constantinople, which lasted until 1261, eleven years after his death.

Frederick’s kingdom of Sicily had been part of the Byzantine Empire in the past. In Frederick's time, it encompassed the actual island of Sicily as well as most of southern Italy. Both were part of the Byzantine Empire until the 9th century, when Muslims from North Africa gradually invaded. In the 11th century Sicily was conquered again by the Normans, who also took over southern Italy. Under the Normans everyone lived relatively peacefully and there was a mixed Greek-Arab-Norman culture, and the government functioned in all three official languages.

That didn’t last too long though. The Norman king William died with no heirs in 1189, and Sicily eventually passed to his closest relative, his aunt Constance, but only after several years of rival claimants and civil war. Constance was married to the Holy Roman Emperor, Henry VI. He died in 1197 and Constance died in 1198, so their son Frederick became king of Sicily when he was about 4 years old. (He didn’t become King of Germany officially until 1215, and not emperor until 1220 - but that’s a long and separate story!)

Some of the nobles of Sicily didn’t want to be ruled by a foreigner (even though Frederick was actually born in Italy), and the rest of western Europe didn’t think it was a great idea for one person to rule both Sicily and the empire. The popes were especially opposed because if Sicily was part of the empire, then the Papal States in central Italy would be surrounded. So, technically, Sicily was always a separate kingdom.

Meanwhile, some of the Greek and Muslim inhabitants fled after 1189, and the remaining Muslims were all moved to a new colony on mainland Italy during Frederick’s reign. The Greeks on the mainland were also less connected to Constantinople after the Normans took over and the popes in Rome tried to spread Latin Catholicism there, and of course after 1204 there was no Byzantine Empire in Constantinople to support them.

Aside from the disputes over Sicily and the empire Frederick’s entire life was full of other distractions. He married Queen Isabella II of Jerusalem, who died giving birth to their son Conrad, so Frederick claimed to be regent of Jerusalem as well. He promised to go on crusade to Jerusalem but there were frequent delays. He had a lot of enemies and it wasn’t really safe for him to leave all his territory. One of these enemies was the pope, who excommunicated him for not going on crusade. He did finally go on crusade, and even recovered Jerusalem through a peace treaty with Egypt, but the local nobles didn’t want him hanging around there claiming to be regent. In 1245 another pope eventually declared that he was no longer emperor. For the last 5 years of his life he had to deal with the consequences of that as well.

So he didn’t have much time to worry about the Byzantine Empire. As far as Frederick was concerned he was the only Roman Emperor. Not just the “Roman emperor of the German nation” or the “German emperor”, as the Holy Roman Emperors were usually known when they interacted with the Byzantine emperors, but the sole Roman Emperor, since the eastern half of the empire had been destroyed. There may still have been some Greek influence on Sicily; he issued new laws, the “Constitutions of Melfi”, which were partly inspired by Roman and Byzantine law, but were mostly based on Norman law and Frederick’s own innovations. He also wrote a book about hunting with birds, which may have had some minor Byzantine (and Arab) influences. For the most part he wasn’t really influenced by the (non-existent) Byzantine Empire.

“Frederick had no real interest in the Greek Church of Italy or of the Byzantine world. Constantinople had ceased after the Latin conquest of 1204 to act as the international centre of a cosmopolitan culture whose reserves of knowledge were unrivalled in the Christian world…Frederick wore a different imperial crown of his own, and the Latin emperor of Constantinople was accorded none of the status that even westerners had recognized the Roman emperors of the East to possess. Frederick kept on good terms with the Lascarid emperor of Nicaea, ruler of a rump state that resisted Frankish conquest, but this was just one element in a Mediterranean policy whose emphasis lay elsewhere.” (Abulafia, 253)

Frederick seems to have felt that both he and the rulers of Nicaea (and the other Byzantine successor state in Epirus) were victims of unjust Papal attacks. He may have wanted to help restore the Byzantine Empire, simply as a way to snub the Pope. In 1244 the ruler of Nicaea, John III Vatatzes, married Frederick’s daughter Constance, so there may have been a chance for further cooperation if Frederick hadn’t been distracted by his dispute with the Pope. His friendship with John Vatatzes was actually one of the very long list of reasons he was deposed in 1245.

Sources:

David Abulafia, Frederick II: A Medieval Emperor (Oxford University Press, 1992)

Donald M. Nicol, The Last Centuries of Byzantium, 1261-1453, 2nd ed. (Cambridge University press, 1993)