[13] Jenő Szűcs argued that Béla IV – who attempted to restore royal authority and revise his predecessors' land grants in Hungary – strongly opposed Stephen's generous donations to his own partisans (for instance, Denis Péc) in Styria, which strained their relationship.

According to Sălăgean, Stephen, who represented a "late medieval chivalry", could select appropriate combat-capable accompaniment from the young members of lesser noble families (e.g. Reynold Básztély, Egidius Monoszló and Mikod Kökényesradnót).

[19] Jenő Szűcs emphasised that Stephen, as Duke of Transylvania, began using the denotation "dei gratia" (by the Grace of God) arbitrarily before the list of his titles, which was used exclusively by the reigning kings in Hungary.

Anna's sons, Michael and Béla, accused Stephen of confiscating their castles – Bereg (Munkács) and Füzér – violating the 1262 Treaty of Pressburg, which, according to Zsoldos, was incapable of resolving the dynastic conflict.

According to Jenő Szűcs, although this intersection of territorial and personal principles was not unheard of in the classical fidelity structure, it was alien to Hungarian experience and therefore created the legal conditions for the development of feudal anarchy.

[54] According to historian Attila Zsoldos, Béla IV – having secured himself on several fronts – confronted his elder son at the event, which made a large-scale civil war in Hungary inevitable.

They invaded Duke Stephen's realm and pushed forward unhindered penetrating to the valley of the Maros (Mureș) river in the southern part of Transylvania,[56][57] despite the failed efforts of Alexander Karászi to regain these territories.

[58] Stephen's army – the younger king was present in person, along with Peter Csák and Mikod Kökényesradnót – stopped their advance at the Fortress of Déva (Deva, present-day Romania), where the invaders suffered a heavy defeat, and Julius Kán was killed.

Just before the Kán brothers' attack, Stephen began to gather his army and left his family – Queen Elizabeth, his four daughters and the infant son Ladislaus – behind the fortified walls of Patak Castle in Zemplén County (today in ruins near Sátoraljaújhely).

[25][63] Simultaneously with the military events in the Maros valley, another royal army crossed the border from the Szepesség region (Spiš) on the shortest route to the northeast under Duchess Anna's command in Upper Hungary.

Stephen's family were transferred to Turóc Castle (also known as Znió or Zniev, present-day near Kláštor pod Znievom, Slovakia), in the realm of Béla IV, guarded by Andrew Hont-Pázmány on orders from Duchess Anna who most fervently opposed her brother's aspirations.

For instance, Béla's troops occupied the castle of Ágasvár, a small fort in the mountain range of Mátra in Nógrád County, almost without resistance because of the "unbelief and unfaithful negligence" of Job Záh, the Bishop of Pécs, who surrendered.

[65] A certain Bács (Bach) – brother of ispán Tekesh – also handed over the castle of Szádvár in Torna County, preventing a protracted siege and opening the gates before Henry Kőszegi's advancing troops.

Zsoldos identified "Temethyn", consisting of ditches and ramparts, with a recently excavated fortified outpost at the top of the Őrhegy ("Guard Hill") about one kilometre from the caste of Füzér (The word "temetvény" originally meant "embankment").

For instance, he lent Elizabeth 100 silver marks during her captivity and allowed the duke's courier Emeric Nádasd to inform Stephen quickly of the fall of Patak and the house arrest of his family.

Peter Csák successfully recaptured the fort of Baranka from Duchess Anna's troops, but his small army was unable to achieve further victories and could not prevent the permanent internment of Queen Elizabeth and the children in Béla's domain.

[72] However, some nobles, led by Panyit Miskolc, who were forced to enlist in the royal army during the early stage of civil war, switched allegiance and reconnoitred the besiegers' intentions, defeating them with "strength and cunning".

[72] Through his victory at Feketehalom and the prior endeavours of Peter Csák, Stephen instantly regained control over Transylvania and its attached territories, Szatmár, Bereg and Ung counties, which allowed the rapid mobilisation to Northeast Hungary.

Several of his partisans joined the army along its route, including Michael Rosd,[76] Peter Kacsics with his banderium (military unit) from Nógrád County and Stephen Rátót, who administered the queenly castle folks.

[60] According to Attila Zsoldos, Stephen's army marched into Hermannstadt (Szeben) then Kolozsvár (present-day Sibiu and Cluj-Napoca, Romania), before crossing the King's Pass (Hungarian: Király-hágó, Romanian: Pasul Craiului) from Transylvania to Tiszántúl ("Transtisia").

It is plausible, because the prolonged siege of Feketehalom had failed by then, that Henry Kőszegi sent his lieutenant Ernye Ákos and his troops to conquer the area, support the besiegers and hinder Duke Stephen's counter-offensive later.

[79] Béla of Macsó was able to flee the battlefield, while Henry Kőszegi was taken prisoner by the young courtly knight, Reynold Básztély, who knocked the powerful lord out of his horse's saddle with his lance and captured him on the ground.

Around the same time, Stephen's sister Kinga of Poland sent a letter to her niece Kunigunda of Halych (Ottokar's spouse) in Prague, in which she regretted the turn of events and lamented the sorrowful fate of her father Béla IV, who "in his bent age, when he should rest[.]

Informed of the adverse military news from the battlefields around late February 1265, the elderly monarch ordered Stephen's only son Ladislaus be sent as a political hostage from Turóc Castle to the court of Béla IV's son-in-law, Boleslaw the Chaste, Duke of Cracow in Poland.

[81] Their peace resulted in status quo ante bellum ("the situation as it existed before the war") and restoration of the 1262 Treaty of Pressburg, i.e. Béla was forced to acknowledge Stephen's suzerainty over the eastern part of Hungary (including the Cumans again).

[90] The new treaty confirmed the division of the country along the Danube and regulated many aspects of the co-existence of Béla's regnum and Stephen's regimen (the only distinction in terminology that refers to the latter's formal subordination), including the collection of taxes and the commoners' right to free movement.

Another Austrian annales, the Historia Annorum (written by Gutolf von Heiligenkreuz in the 1280s) lists the victories of Stephen during the civil war under this year too, possibly based on a donation letter from Hungary.

[109] Based on contemporary charters and documents, Hungarian historian Gyula Pauler determined the date of the civil war at the turn of 1264 and 1265 in his seminal monograph A magyar nemzet története az Árpádházi királyok alatt, Vol.

The historian connected this information to an inventory of an 18th-century list and extract of the documents of the Kleinmariazell Abbey; a short note in the manuscript contains a brief description of a 1267 charter, in which a certain Austrian ministerialis Gundakar von Hassbach undertook to donate his estate called Rohrbach to the monastery in case he did not return "from the Hungarian war".

According to Zsoldos, Gundakar von Hassbach's departure to Hungary in 1267 connects to those events, when Béla IV tried unsuccessfully to prepare for another war against his son during the Esztergom meeting in the summer of that year.