William II’s foreign policy (the two empires)

Despite the internal problems of the regency, which ended in 1171, its foreign policy remained ambitious. Its alliance with the papacy continued and its struggle against the hegemony of the German emperor persisted. The Eastern emperor seeking an alliance with the Norman king offered his daughter, Marie, (1171) in marriage, but as she did not arrive in Italy, this was seen as a snub to William II.
The German emperor increased his raids in Italy, but Frederick Barbarossa’s fifth attempt, between 1174 and 1176 again ended in failure. The Pope, still supported by the Normans, excommunicated the emperor Barbarossa, who had to negotiate with Alexander III, the Lombard northern princes and the Normans. (July 1177).
With the subjugation of the barons, the Norman king resumed his grandfather’s, Roger II, policy in the East, but in 1174, the Normans failed, following an appeal from the king of Jerusalem, to take Alexandria.
In 1180, following the death of the Eastern emperor Manuel Comnenus, the regency was assumed by his wife, Mary of Antioch, the great-grand daughter of the Norman Bohemond, which exacerbated, in Byzantium, Greek resentment against the Latins. Then, William II of Sicily, decided to create a grand alliance against Byzantium and, in 1184, betrothed, Roger II’s daughter, his aunt Constance de Hauteville (30 years old), to the eldest son of Frederick I Barbarossa, the future Henry VI (18 years old).
The following year the Normans attacked Durazzo again, their fleet conquered Corfu, Cephalonia and Zante, and also captured Byzantium’s second city, Thessalonica. Following his defeat, Emperor Andronicus Comnenus was lynched by a mob in Constantinople and succeeded by Issac II Angelus. Nevertheless, in November, the Byzantine army defeated the Normans, who, though forced to retreat, managed to keep Cephalonia and Corfu.