Excerpts from Books and Wikipedia
"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 sent two leaders (Peter and Asen) to negotiate with the emperor at Kypsella (now Ipsala) in Thrace. 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. This was refused, and Peter and Asen were treated roughly. Their response was to threaten revolt." [Wikipedia]