It began on 26 October 1185, the feast day of St. Demetrius of Thessaloniki, and ended with the restoration of Bulgaria with the creation of the Second Bulgarian Empire, ruled by the Asen dynasty.

Isaac II Angelus, in order to raise money for his wedding with the daughter of King Béla III of Hungary, levied a new tax which fell heavily on the population of the Haemus Mountains.

They asked to be added to the roll of the Byzantine army and to be granted land near Haemus to provide the monetary income needed to pay the tax.

During the solar eclipse of 21 April 1186, the Byzantines successfully attacked the rebels, many of whom fled north of the Danube, making contact with the north-Danubian Vlachs and with the Cumans of the Pontic Steppe.

The Emperor's only consolation was to hold, as hostages, Asen's wife and a certain John (future Kaloyan of Bulgaria), brother of the two new leaders of the Bulgarian state.