Byzantine–Hungarian War (1162–1167)

After the previous Byzantine–Hungarian War, king Géza II signed a five-year truce with the Byzantine Empire in 1161. However, his death in the following year sparked a succession crisis between his son, Stephen III, and his exiled uncles, Ladislaus II and Stephen IV, who were supported by Emperor Manuel I Komnenos. Manuel sheltered Géza's other son, Béla, in Constantinople and granted him the title of despot, along with appanage claims over Dalmatia, Croatia, and Sirmium. This manifested in Manuel's military presence on the Danube frontier in 1163, pressuring Stephen III, as Hungarian loyalists resisted the Byzantine-backed claimants.

A provisional peace treaty in 1163 saw Manuel renounce overt aid to Stephen's domestic opponents, in exchange for Hungarian recognition of Byzantine suzerainty over the disputed Balkan territories. However, Stephen III quickly violated these terms by resuming hostilities and fostering alliances with the Serbian principalities. This reignited skirmishes along the Danube frontier. Hungarian forces subsequently launched incursions into Byzantine-held Dalmatia in 1164, seizing key coastal holdings like Split, in defiance of the treaty. The situation escalated into mutual raids that disrupted trade routes and endangered cities.

By 1165–1166, due to entrenched distrust over territorial concessions, Stephen III refused to cede control of Dalmatia and Sirmium to Béla, viewing it as an infringement on Hungarian sovereignty, while Manuel interpreted Hungarian-Serbian alliances as direct threats to imperial holdings, prompting retaliatory Byzantine expeditions that failed to secure lasting compliance. Hungarian aggression in Sirmium began with a war council at Sardica, where generals debated the campaign's leadership amid Emperor Manuel's deteriorating health. Command was delegated to Manuel's nephew, the Megas Doux Andronikos Kontostephanos, who assembled the army during the spring. The opposing armies met near Sirmium in July 1167. The Byzantine army deployed in three main divisions; the centre under Kontostephanos himself, incorporating the core guards and bodyguard units; the left wing arrayed in four taxiarchies of regular and allied troops, led by Demetrios Branas, George Branas, Tatikios Aspietes, and Kogh Vasil; and the right wing with elite native cavalry, German mercenaries, and Turkoman units under Andronikos Lapardas (possibly alongside John Kontostephanos). The Hungarian forces, under Dénes of Bács, consisting approximately 15,000 men, launched a primary assault in the early morning hours, seeking to overwhelm the Byzantine lines with a heavy cavalry charge, which initially disrupted the Byzantine left wing, but which in turn executed a tactical feigned retreat toward the Sava River, drawing the attackers deeper into vulnerable positions. The Hungarian momentum faltered as they encountered the disciplined counteraction of Byzantine pronoiarii heavy cavalry lancers, whose cohesive charges and subsequent melee with maces, shattered the Hungarian formation. The Hungarian army would eventually be routed, while suffering heavy losses following the counterattack, resulting in a decisive victory for the Byzantines.

Following their defeat after the battle of Sirmium, the Hungarians sued for peace on Byzantine terms and recognized the empire’s control over Bosnia, Dalmatia, Croatia south of the Krka River, as well as the Fruška Gora. When Stephen died in 1172, Béla succeeded him after being deprived of his title of despot and position as heir to the imperial throne that same year. Hungary would agree to pay tribute and supply troops upon request and provide hostages to ensure their continued compliance to the Byzantine Empire. Béla had to swear an oath that he would never harm Manuel as long as he lived, until his death in September of 1180;^[3] after which he would later conquer and annex those lands held previously by the Byzantines, after he was requested by Maria of Antioch for aid against Andronikos I Komnenos. To protect her regency of her son, Alexios II Komnenos, Maria later recognized Hungarian territorial claims on certain Byzantine lands in exchange for Béla's support.