In June 1185, William II of Sicily and an army of eighty thousand men sailed from Messina to Durazzo and by 8th August was encamped outside Thessalonica. The Byzantine Emperor Andronicus Comnenus was caught unawares. The city fell amongst scenes of wholesale slaughter.
In Constantinople the citizens were in a state of panic. A guard was sent to arrest the Emperor's cousin Isaac Angelus, but Isaac killed the guard and rushed to St Sophia to raise the citizens to revolt. Andronicus fled in a galley up the Bosphorus. He was soon caught and brought before Isaac for punishment. His right hand was cut off, he was blinded in one eye and left to starve.
Isaac sent his most ablest general, Alexius Branas, to deal with the Sicilians, whose fleet was already in the sea of Marmara. Branas drove the Sicilians back to Amphipolis. Meanwhile, the citizens of Thessalonica rose up and wreaked revenge on their oppressors. Some Sicilians managed to find their way home but most died.
Although the reign of Andronicus had been violent, he had at least stamped out corruption. Isaac, however, 'sold government offices like vegetables in a market'. He showed great energy in putting down rebellions and protecting his frontiers, but he was unable to prevent the rise of the Second Bulgarian Empire and in 1190 his army was ambushed and he only just escaped with his life.
In May 1187, the Saracens under Saladin crossed the Jordan into Frankish territory and defeated the army of Guy of Lusignan at the Horns of Hattin. In October 1187 Saladin took Jerusalem. When the news reached the West, Pope Urban III died of shock and his successor, Gregory VIII, declared another Crusade. Leading it would be Byzantium's old enemy Frederick Barbarossa and William of Sicily. William died in November 1189, but the crown of Sicily passed to Barbarossa's eldest son, Henry. Also participating were Richard Coeur-de-Lion of England who was William's brother-in-law, and Philip Augustus of France who also had reason to dislike Byzantium.
Richard and Philip travelled to the Holy land by sea, Richard taking time out on the way to take Cyprus from Isaac, May 1191. Frederick Barbarossa set out on the land route in May 1189 with an army of 150,000 men. With the Serbs and Bulgars declaring allegiance to Frederick against Byzantium, Isaac sent Constantine Cantacuzenus and John Ducas to meet the great army at the frontier. However they too turned against their master. When Frederick sent envoys to Isaac to discuss the transport of the Crusaders to Anatolia, Isaac had them thrown in prison. Only when threatened with a crusade against himself did he relent and allowed transport across the water, although only by the Dardenelles rather than the Bosphorus, thus avoiding Constantinople altogether.
On 10 June 1190, after a long and exhausting journey across Anatolia, Frederick Barbarossa rode to the nearest river, dismounted or fell off and was drowned. His army soon disintegrated. Richard and Philip Augustus were more successful although they didn't manage to re-capture Jerusalem.
On Christmas Day, 1194, Frederick Barbarossa's son Henry (Holy Roman Emperor Henry VI) was crowned King of Sicily in Palermo Cathedral. He was already planning another Crusade and in 1195 wrote to Isaac, with a number of unrealistic demands. However, on 8th April 1195 Isaac Angelus fell victim to a coup engineered by his elder brother Alexius, who deposed him, blinded him and seized the throne.