Bela IV
Bela IV was the king of Hungary and Croatia.
History
Bela IV was the eldest son of Andrew II.
In 1220 he married Maria, a daughter of Theodore I Laskaris, emperor of Nicaea.
Bela was appointed duke of Slavonia in 1220, but was absent from 1222 until 1223; Andrew demanded that he separate from Maria but Pope Honorius III refused to annul the marriage. Bela fled to Austria briefly.
In 1226, Andrew transferred Bela to the duchy of Transylvania. He expanded into Cumania amidst the Mongol invasion.
Reign
Andrew II died on September 21, 1235. Bela was quickly crowned. He consolidated control by seizing land grants and royal charters.
As the Cumans fled Mongol expansion, Bela welcomed them into Hungary with the conditions that they convert and help repel the Mongols. Ethnic violence persisted against the Cumans however, leading them to abandon Hungary right as the Mongols reached Pest. The Hungarian army was soundly defeated.
Bela fled to Austria, where he was compelled to give suzerainty and cede counties including Bratislava to Frederick II.
Ogedei died in December 1241, leading the Mongols to return to Karakorum in early 1242 for the election of the next khan.
Bela returned to Hungary in May 1242 and began to rebuild and fortify the kingdom in anticipation of another invasion. He constructed castles along the border and established Buda as the capital with a new castle hill. 15% of the Hungarian population had died in the invasion and subsequent famine; he encouraged the Cumans to return and incentivized colonization with greatly expanded town rights and favorable taxes.
In 1245, Pope Innocent IV annulled the pledge Bela had made to Frederick, who retaliated the next year but died in his invasion. After a decade of war, Styria would be ceded to Bela in 1254. In 1260, the local nobility would rise up and force him to renounce the duchy in favor of Ottokar II.
Bela also invaded the Bulgaria to the south. Belgrade was ceded to him in 1255.
Bela IV attempted to expand his control over neighboring kingdoms by marrying his daughters into their ruling dynasties. His eldest daughter St. Kunegunda was married to Bolesław V, the high duke of Poland. Anna was married to Rostislav Mikhailovich, a claimant to the principality of Halych. Elizabeth (Erzsebet) was married to Henry XIII, duke of Bavaria. Constance (Konstancia) was married to Leo I, another claimant to the principality of Halych that would go on to have much more success in said claiming. He attempted to marry St. Margaret (Margit) to Ottokar, but she took monastic vows to avoid the marriage. His granddaughter Kunigunda, by way of Anna, was married to Ottokar instead.
Bela IV died on May 3, 1270.
Legacy
Bela IV greatly expanded the military power and defensive capabilities of Hungary.