To convince their compatriots to join them, they had native prophets declare that Saint Demetrius of Thessalonica had abandoned the Romans in favour of the Bulgarians and Vlachs.

Returning in the autumn at the head of Cuman troops, they took control of Paristrion, firmly establishing the new state, regarded as the successor to the First Bulgarian Empire.

[13][14] The presence of many ethnic groups in the lands to the south of the Lower Danube in the 12th century is well documented, thus they were most likely of mixed Vlach, Bulgarian and Cuman origin.

[22][23] Choniates' words show that the brothers wanted to receive a pronoia grant (that is, the revenues from an imperial estate in exchange for military service).

[6] Theodor-Peter and Asen decided to take advantage of the Bulgarians and Vlachs' devotion to the cult of the martyr saint Demetrius of Thessaloniki to persuade them to rise up against the Byzantine rule.

[23] At the brothers' instruction, the soothsayers announced "in their ravings" that God had consented to the uprising against the Byzantines, and Saint Demetrius would abandon Thessaloniki and "come over to them to be their helper and assistant" during the forthcoming rebellion.

[39] Heartened by the victories, Theodor-Peter "bound his head with a gold chaplet and fashioned scarlet buskins to put on his feet",[40] thus adopting insignia that had been used only by the emperors.

[42][43][44] Madgearu says, the coronation most probably took place before the end of 1185, because a priest, Basil, was allegedly made the head of the restored Bulgarian Orthodox Church in that year.

[46][47] The rebels again stormed into Thrace and carried away "many free [people], much cattle and draft animals, and sheep and goats in no small number" in early 1186.

[40][48] To prevent the rebels from crossing the mountain passes, Isaac II launched a campaign against them, but they occupied "the rough ground and inaccessible places"[40] and resisted the attacks.

[49] However, a sudden "blackness" (associated with the solar eclipse of 21 April 1186) rose up and "covered the mountains",[50] enabling the Byzantines to inflict a severe defeat on the rebels.

[43][52] The imperial troops "set up fire to the crops gathered in heaps" by the local inhabitants, but made no major efforts to capture the rebels' fortresses which were "built on sheer cliffs and cloud-capped peaks".

[43][53][54] Isaac II also failed to garrison the castles along the Lower Danube, enabling the refugees to return, accompanied by Cuman troops in the autumn of 1186.

[16][55] Theodor-Peter had promised rich booty and salary to the Cumans to talk them into supporting him, according to a letter that Niketas Choniates wrote on the emperor's name a year after the events.

[60][61] According to a scholarly theory, Isaac II acknowledged the independence of the territories under the rule of Theodor-Peter and Asen in a peace treaty signed in the summer of 1188.

[67][69] He sent a second envoy to Barbarossa, who had come into conflict with Isaac II, to Adrianople (now Edirne in Turkey) in December, offering "forty thousand Vlachs and Cumans armed with bows and arrows"[70] to fight against the Byzantines.

[73][74] On the day when the treaty was concluded, Isaac II's envoy tried to talk Barbarossa into a joint military action against the Vlachs, while Theodor-Peter's delegate again proposed an alliance against the Byzantines.

[77] In July 1190, he invaded the brothers' realms across the Rish Pass and dispatched a fleet to the Lower Danube to prevent the Cumans from crossing the river.

[8] Isaac II escaped, but much of the army perished and the victors seized "the more valuable of the emperor's insignia",[80] including his pyramidal crown and relics associated with the Virgin Mary.

[92] The emperor dispatched Manuel Kamytzes to lead an army to Tarnovo, but fear of an ambush at the mountain passes led to an outbreak of mutiny and the troops forced him to return.

[98] Historian István Vásáry writes, Theodor-Peter was killed during a riot;[94] Stephenson proposes, the native lords got rid of him, because of his close alliance with the Cumans.