Stephen V of Hungary

Seal of Stephen's wife, Elizabeth the Cuman

A royal charter of 1246 mentions Stephen as "King, and Duke of Slavonia".[4] Apparently, in the previous year, Béla had his son crowned as junior king and endowed with the lands between the river Dráva and the Adriatic Sea, according to historians Gyula Kristó and Ferenc Makk.[4][8] The seven-year-old Stephen's provinces—Croatia, Dalmatia and Slavonia—were administered by royal governors, known as bans.[4][9]

In a letter addressed to Pope Innocent IV in the late 1240s, Béla IV wrote that "[o]n behalf of Christendom we had our son marry a Cuman girl".[10] The bride was Elizabeth, the daughter of a leader of the Cumans whom Béla had invited to settle in the plains along the river Tisza.[11][12] Elizabeth had been baptized, but ten Cuman chieftains present at the ceremony nevertheless took their customary oath upon a dog cut into two by a sword.[13]

When Stephen attained the age of majority in 1257, his father appointed him Duke of Transylvania.[2][14] Stephen's rule in Transylvania was short-lived, because his father transferred him to Styria in 1258.[8][14] Styria had been annexed in 1254, but the local lords rose up in rebellion and expelled Béla IV's governor, Stephen Gutkeled, before Stephen's appointment.[15] Stephen and his father jointly invaded Styria and subdued the rebels.[16] In addition to Styria, Stephen also received two neighboring counties—Vas and Zala—in Hungary from his father.[16][17] He launched a plundering raid in Carinthia in the spring of 1259, in retaliation of Duke Ulrich III of Carinthia's support of the Styrian rebels.[16][18]

Stephen's rule remained unpopular in Styria. With support from King Ottokar II of Bohemia, the local lords again rebelled.[19] Stephen could preserve only Pettau (present-day Ptuj, Slovenia) and its region.[20] On 25 June 1260, Stephen crossed the river Morava to invade Ottokar's realm.[21] His military force, which consisted of Székely, Romanian and Cuman troops, routed an Austrian army.[21][22] However, in the decisive Battle of Kressenbrunn King Béla's and Stephen's united army was vanquished on 12 July, primarily because the main forces, which were under King Béla's command, arrived late.[23][22] Stephen, who commanded the advance guard, barely escaped from the battlefield.[24] The Peace of Vienna, which was signed on 31 March 1261, put an end to the conflict between Hungary and Bohemia, forcing Béla IV to renounce of Styria in favor of Ottokar II.[23]

Baba Vida, the medieval fortress at Vidin in Bulgaria: Stephen captured it in 1261

Stephen returned to Transylvania and started to rule it for the second time after 20 August 1260.[14][23] He and his father jointly invaded Bulgaria and seized Vidin in 1261.[2] His father returned to Hungary, but Stephen continued the campaign alone.[25] He laid siege to Lom on the Danube and advanced as far as Tirnovo in pursuit of Tsar Constantine Tikh of Bulgaria.[25] However, the Tsar succeeded in avoiding any clashes with the invaders and Stephen withdrew his troops from Bulgaria by the end of the year.[25]

Stephen's relationship with Béla IV deteriorated in the early 1260s.[26] Stephen's charters reveal his fear of being disinherited and expelled by his father.[26] He also accused some unnamed barons of inciting the old monarch against him.[26] On the other hand, Stephen's charters prove that he made land grants in Bihar, Szatmár, Ugocsa, and other counties which were situated outside Transylvania.[27]

Stephen V is crowned by his father, Béla IV (from the Illuminated Chronicle)

Archbishops Philip of Esztergom and Smaragd of Kalocsa undertook to mediate after some clashes occurred between the two kings' partisans in the autumn.[28][29] According to the Peace of Pressburg, which was concluded around 25 November, Béla IV and his son divided the country and Stephen received the lands to the east of the Danube.[30][31] When confirming the treaty on 5 December, Stephen also promised that he would not invade Slavonia which had been granted to his younger brother, Béla, by their father.[28] On this occasion, Stephen styled himself "Junior King, Duke of Transylvania and Lord of the Cumans".[30][28]

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.[32][33] Stephen sent reinforcements under the command of Ladislaus II Kán, Voivode of Transylvania to Bulgaria.[33] The Voivode routed the Byzantines and drove them out of Bulgaria.[34] Stephen granted Vidin to Jacob Svetoslav who accepted his suzerainty.[34]

The reconciliation of Stephen and his father was only temporary.[35] Stephen confiscated the domains of his mother and sister, Anna—including Beszterce (present-day Bistrița, Romania) and Füzér—which were located in the lands under his rule.[31] Béla IV's army crossed the Danube under Anna's command sometime after the autumn of 1264.[31][36] She besieged and took Sárospatak and seized Stephen's wife and children.[36] Voivode Ladislaus Kán turned against Stephen and led an army, which consisted of Cuman warriors, to Transylvania.[37] Stephen routed him at the fort of Déva (now Deva, Romania).[30][36] King Béla's Judge royal, Lawrence arrived at the head of a new army and forced Stephen to retreat to Feketehalom (now Codlea, Romania).[38][36] The Judge royal lay siege to the fortress, but Stephen's partisans relieved it.[38][36] Stephen launched a counter-offensive and forced his father's army to retreat.[35][39] He gained a decisive victory over his father's army in the Battle of Isaszeg in March 1265.[19][36] The two archbishops mediated a new consolidation between father and son, which confirmed the 1262 division of the country.[40] Béla and Stephen signed the peace treaty in the Convent of the Blessed Virgin on the Rabbits' Island (now Margaret Island in Budapest) on 23 March 1266.[41][35]

During the civil war in Hungary, Stephen's vassal, Despot Jacob Svetoslav submitted himself to Tsar Constantine Tikh of Bulgaria.[42] In the summer of 1266, Stephen invaded Bulgaria, seized Vidin, Pleven and other forts and routed the Bulgarians in five battles.[41][43] Jacob Svetoslav again accepted Stephen's suzerainty and was reinstalled in Vidin.[43] From then on, Stephen used the title "King of Bulgaria" in his charters.[19]

Béla and Stephen together confirmed the liberties of the "royal servants", from then on known as noblemen, in 1267.[44] A double marriage alliance between Stephen and King Charles I of Sicily—Stephen's son, Ladislaus married Charles's daughter, Elisabeth, and Charles's namesake son married Stephen's daughter, Mary—strengthened Stephen's international position in 1269.[44][45] Confidence was never restored between Béla and Stephen.[45] On his deathbed, the old King requested King Ottokar II of Bohemia to give shelter to his daughter Anna and his partisans after his death.[45][46]