Ivan Asen I of Bulgaria in the context of "Vlachs"

The Byzantine–Bulgarian wars were a series of conflicts fought between the Byzantine Empire and the Bulgarian Empire which began after the Bulgars conquered parts of the Balkan peninsula after 680 AD. The Byzantine and First Bulgarian Empire continued to clash over the next century with varying success, until the Bulgarians, led by Krum, inflicted a series of crushing defeats on the Byzantines. After Krum died in 814, his son Omurtag negotiated a thirty-year peace treaty. Simeon I had multiple successful campaigns against the Byzantines during his rule from 893 to 927. His son Peter I negotiated another long-lasting peace treaty. His rule was followed by a period of decline of the Bulgarian state.

In 971 John I Tzimiskes, the Byzantine emperor, subjugated much of the weakening Bulgarian Empire by defeating Boris II and capturing Preslav, the Bulgarian capital. Samuel managed to stabilize the Bulgarian state with its center around the town of Prespa. Near the end of his rule, the Byzantines regained the upper hand, and under Basil II they won the Battle of Kleidion and completely conquered Bulgaria in 1018. There were rebellions against Byzantine rule from 1040 to 1041, and in the 1070s and the 1080s, but these failed. In 1185, however, Theodore Peter and Ivan Asen started a revolt, and the weakening Byzantine Empire, facing internal dynastic troubles of its own, was unable to quash the revolt.

The Uprising of Asen and Peter (Bulgarian: Въстание на Асен и Петър) was a revolt of Bulgarians and Vlachs living in Moesia and the Balkan Mountains, then the theme of Paristrion of the Byzantine Empire, caused by a tax increase. 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 İpsala) 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.

Ivan Asen II, also known as John Asen II (Bulgarian: Иван Асен II, [iˈvan ɐˈsɛn ˈftɔri]; 1190s – May/June 1241), was Emperor (Tsar) of Bulgaria from 1218 to 1241. He was still a child when his father Ivan Asen I – one of the founders of the Second Bulgarian Empire – was killed in 1196. His supporters tried to secure the throne for him after his uncle, Kaloyan, was murdered in 1207, but Kaloyan's other nephew, Boril, overcame them. Ivan Asen fled from Bulgaria and settled in the Rus' principalities.

Boril could never strengthen his rule which enabled Ivan Asen to muster an army and return to Bulgaria. He captured Tarnovo and blinded Boril in 1218. Initially, he supported the full communion of the Bulgarian Church with the Papacy and concluded alliances with the neighboring Catholic powers, Hungary and the Latin Empire of Constantinople. He tried to achieve the regency for the 11-year-old Latin Emperor, Baldwin II, after 1228, but the Latin aristocrats did not support Ivan Asen. He inflicted a crushing defeat on Theodore Komnenos Doukas of the Empire of Thessalonica, in the Battle of Klokotnitsa in 1230. Theodore's empire soon collapsed and Ivan Asen conquered large territories in Macedonia, Thessaly and Thrace.

Peter II, born Theodor, also known as Theodor-Peter (Bulgarian: Теодор-Петър; died in 1197), was the first emperor or tsar of the restored Bulgarian Empire from 1185 to 1197. He hails from the Byzantine theme of Paristrion, although his exact place and date of birth are unknown.

He and his younger brothers, Asen and Kaloyan, were mentioned as Vlachs in most foreign contemporaneous sources but they were probably of a mixed Vlach, Bulgarian, and Cuman origin. In 1185, Theodor and Asen approached the Byzantine Emperor Isaac II Angelos in Thrace, demanding an estate in the Balkan Mountains. After the Emperor refused and humiliated them, they decided to incite a rebellion, taking advantage of the discontent that a new tax had caused among the Bulgarians and Vlachs. 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. Before the end of the year, Theodor was crowned Emperor of Bulgaria, taking the name Peter and adopting the insignia used only by emperors.

Kaloyan or Kalojan, also known as Ivan I, Ioannitsa or Johannitsa (Bulgarian: Калоян, Йоаница; c. 1170 – October 1207), the Roman Slayer, was emperor or tsar of Bulgaria from 1196 to 1207. He was the younger brother of Theodor and Asen, who led the anti-Byzantine uprising of the Bulgarians and Vlachs in 1185. The uprising ended with the restoration of Bulgaria as an independent state. He spent a few years as a hostage in Constantinople in the late 1180s. Theodor, crowned Emperor Peter II, made him his co-ruler after Asen was murdered in 1196. A year later, Peter was also murdered, and Kaloyan became the sole ruler of Bulgaria.

After the successful siege of Varna in 1201 against the Byzantine Empire, the defenders and governors of the city were tied and thrown into the moat of the fortress walls and covered with dirt by the Bulgarians. After they were buried alive in this way, Kaloyan declared himself a Bulgarian avenger, adopting the moniker "the Romanslayer" by analogy with the emperor Basil II the Bulgar Slayer, who defeated and blinded a Bulgarian army of 15,000 people.

Boril (Bulgarian: Борил) was the emperor (tsar) of Bulgaria from 1207 to 1218. He was the son of an unnamed sister of his predecessor, Kaloyan and Kaloyan's brothers, Peter II and Ivan Asen I, who had restored the independent Bulgarian state. After Kaloyan died unexpectedly in October 1207, Boril married his widow, a Cuman princess and seized the throne. His cousin, Ivan Asen, fled from Bulgaria, enabling Boril to strengthen his position. His other kinsmen, Strez and Alexius Slav, refused to acknowledge him as the lawful monarch. Strez took possession of the land between the Struma and Vardar rivers with the support of Stefan Nemanjić of Serbia. Alexius Slav secured his rule in the Rhodope Mountains with the assistance of Henry, the Latin Emperor of Constantinople.

Boril launched unsuccessful military campaigns against the Latin Empire and the Kingdom of Thessalonica during the first years of his reign. He convoked the synod of the Bulgarian Church in early 1211. At the assembly, the bishops condemned the Bogomils for heresy. After an uprising broke out against him in Vidin between 1211 and 1214, he sought the assistance of Andrew II of Hungary, who sent reinforcements to suppress the rebellion. He made peace with the Latin Empire in late 1213 or early 1214. After Henry died in 1216 and Andrew II left Hungary for a crusade, Ivan Asen returned to Bulgaria. He captured and blinded Boril in Tarnovo in 1218.