The Byzantine Empire
Alexius III Angelus (1195-1203)
Alexius III Angelus had to deal almost immediately with the German threat. Henry VI was demanding that Byzantium yield the territories conquered by the Normans, by virtue of Henry's claims through his Norman wife. Moreover, Henry's brother Philip of Swabia was married to Irene, the daughter of the now-deposed Isaac II, giving Henry a second claim and reason to invade. Henry's grand plan was to invade and conquer the Byzantine Empire, then use that as a launching ground for a crusade to the Holy Land. He was claiming that as the heir to the Roman Empire at Rome, his imperial title was superior to the Greek title. The kings of Cyprus and Cilicia were already recognizing his suzerainty.
Henry was able to set his crusade in motion, but he himself died in 1197. Some German armies did march east, but they went to Palestine, not to Byzantium. Fortune again reprieved the Empire. But the reprieve was only temporary. Serbia was restless. Bulgaria threatened. The Turks would take advantage of any unrest. Germany was sunk in civil war, but Venice and the papacy still had powerful reasons to want to take advantage of Constantinople's misfortunes.
When the Fourth Crusade showed up with Alexius IV in tow, ostensibly to restore Isaac II, Alexius III put up a token resistance and then fled the city. The Crusaders installed Isaac and Alexius as co-emperors in 1203, but the Latins and Greeks soon quarreled. One of Alexius III's sons-in law, Alexius Ducas, called Murzuphlus, seized the throne in January 1204, and had Isaac and Alexius imprisoned. Both soon were dead.