The nearly 500-year conflict encompassed the region of Southeast Europe, or what is known today as north-western Serbia, Romania, Moldavia and northwestern Bulgaria and southwestern Ukraine.

In 1185, after the re-establishment of the Bulgarian Empire, both states fought numerous conflicts for control over the provinces of Belgrade, Braničevo, Vidin and the Severin.

In response, the Byzantine Emperor Leo VI's envoy Niketas Skleros met on the Lower Danube with the Hungarian ruling princes Árpád and Kurszán, and they agreed to form an alliance.

That same year, in 894, Hungarian warriors advanced into the Carpathian Basin and Pannonia to aid the Moravians in their fight against the Bulgarians' Frankish allies.

The small but noteworthy communities implanted by the Bulgarians in Transylvania and between the Tisa and Danube did not even have the option of fleeing from the Hungarians, who came in overwhelming force.

The Pechenegs, for their part, preferred to raid the richer lands of the Bulgarians and Byzantines rather than the poorer Carpathian Basin, which was in a state of some turmoil due to the Hungarian conquest.

In 913, Simeon launched the first in a series of military campaigns by which he seized from the Byzantines most of the Balkan Peninsula; six years later, he exchanged his title of Great Khan for that of Czar.

As long as the Pechenegs remained hostile, the Hungarians would not dare to provoke Simeon by seizing his lands north of the Carpathians and the Danube.

In breaking the Bulgars' resistance, the Hungarians were helped not only by their Pecheneg allies but also by the internal struggle — exacerbated by Byzantine meddling — over the succession to Czar Simeon, who died in 927.

Having seized southern Transylvania from the Bulgarians, Bogát's warriors and their servants settled down in Slavic villages along the lower reaches of the Küküllő rivers.

The region between the Mureș, Tisa, and Danube rivers must have come under the rule of a Hungarian gyula by 948, for that was when Emperor Constantine recorded that the Bulgarian cities Orșova, Belgrade, and Sirmium lay near Hungary's borders.

In 948, a sudden turn of events compelled Transylvania's gyula to adopt a policy divergent from that of the ruling prince who had dispatched his nephew, and the harka Bulcsú to Constantinople, to renew the peace treaty; the envoys attached so much importance to the task that they had themselves baptized.

[3][4] Although marriage of the heir to the Bulgarian throne Gavril Radomir to the daughter of the Hungarian ruler had established friendly relation between the two strongest states in the Danube area, the relationship deteriorated after Géza's death.

[10] Taking advantage of the civil war between Emeric and his younger brother Andrew in Hungary, Kaloyan invaded and captured Belgrade, Barancs (now Braničevo in Serbia), and other fortresses.

[14] The Cuman tribes dwelling to the east of the Olt as far as the river Siret agreed to pay a yearly tribute to the kings of Hungary in early 1227.

According to the former, Duke Béla invaded Bulgaria in 1228, possibly because Tsar Ivan Asen II attempted to hinder the conversion of Cumans into Roman Catholicism in the northernmost part of his realm along the border with Hungary.

According to the Bulgarian historiography, based on the works of Vasil Zlatarski and Petăr Nikov, Béla's invasion took place in the spring of 1232, capturing Belgrade and Barancs and unsuccessfully besieging Vidin.

[22][23] Michael Asen accepted Hungarian suzerainty and married an unidentified daughter of Rostislav Mikhailovich, Duke of Macsó, Béla's son-in-law.

[26] Béla's eldest son and heir Stephen, Duke of Styria entrusted his confidant Csák Hahót to lead the Hungarian auxiliary troops consisted of knights from Zala County.

[29] Following the defeat at Kressenbrunn, after which the Hungarians were forced to renounce Styria in favor of Ottokar II of Bohemia, Stephen was re-installed as Duke of Transylvania.

Following a brief skirmish in the autumn of 1262, Stephen forced his father to cede all the lands of the Kingdom of Hungary to the east of the Danube to him – including Transylvania and Severin – and adopted the title of younger king.

A Bulgarian nobleman, Despot Jacob Svetoslav sought assistance from Stephen after his domains, which were situated in the regions south of Vidin, were overrun by Byzantine troops in the second half of 1263.

In response, fearing Bulgarian retribution and lack of Hungarian support should Béla IV come out victorious, Jacob Svetoslav submitted himself to Tsar Konstantin Tih in early 1265.

Following their peace, younger king Stephen invaded Bulgaria in the summer of 1266, as a punitive expedition for Jacob Svetoslav's betrayal and the Bulgarians' attack during the civil war.

He routed the Bulgarians in five battles;[34][35] his confidant Egidius Monoszló led Stephen's army to successfully besiege and capture Tărnovo, also plundering the surrounding areas.

[37] Historian Dániel Bácsatyai, who considered that the civil war between Béla IV and Stephen took place in 1267, presented an alternative chronology of the events.

[39] The death of Stephen V in 1272 meant that he was succeeded by his infant son Ladislaus IV, with the widowed consort and mother of the boy, Elizabeth, as his regent.

The Kingdom of Hungary fell into constant feudal anarchy, when baronial groups fought for supreme power, which has led to the marginalization of foreign policy towards Bulgaria for decades to come.

Possibly in 1273, Hungarian rule in Barancs, west of Jacob Svetoslav's domain, was put to an end by two Cuman–Bulgarian nobles, Darman and Kudelin.

The Hungarian auxiliary troops, consisted of Transylvanian and Cuman contingents, were led by George Baksa after a failed negotiation attempt between Ladislaus IV and Darman near the Hungarian–Serbian border.