Gabriel Bethlen Gabriel Bethlen ( de Iktár ) ( , , ; 1580 – November 15 , 1629 ) was a King of Hungary as Gabriel I ( 1620 - 1621 ) , Prince of Transylvania ( 1613 – 1629 ) , Duke of Opole ( 1622 – 1625 ) and leader of an anti - Habsburg insurrection in the Habsburg Royal Hungary . His last armed intervention in 1626 was part of the Thirty Years ' War . He led an active Protestant - oriented foreign policy . Life . Gabriel Bethlen , the most famous representative of the Iktári branch of the ancient Hungarian Bethlen family , was born at Marosillye ( today Ilia in Romania ) and educated at Szárhegy ( today Lăzarea in Romania ) at the Lázár Castle belonging to his uncle András Lázár . Thence he was sent to the court of the Transylvanian Prince Sigismund Báthory , whom he accompanied on his famous Wallachia n campaign . Subsequently he assisted István Bocskay to become Prince of Transylvania in 1605 and remained his chief counsellor . Bethlen also supported Bocskay ' s successor Gabriel Báthory ( 1608 – 1613 ) , but the prince became jealous of Bethlen ' s superior abilities and Bethlen was obliged to take refuge with the Turks of the Ottoman Empire . Prince of Transylvania . In 1613 , Bethlen led a large army against Prince Báthory , but in the same year Báthory was murdered by two of his officers . Bethlen was placed on the throne by the Ottomans in opposition to the wishes of the Austrian Habsburg Emperor , who preferred a prince who would incline more toward Vienna than toward Ottoman Constantinople . On 13 October 1613 , the Transylvanian Diet at Kolozsvár ( Cluj - Napoca ) , confirmed the choice of the Turkish sultan . In 1615 , Bethlen was also officially recognized by the Emperor Matthias as the Prince of Transylvania in accordance with Treaty of Nagyszombat . The treaty regarded the principality as an inseparable part of Kingdom of Hungary . Bethlen promised in secret that he would help the Habsburgs against the Ottomans . While avoiding the cruelties and excesses of many of his predecessors , Bethlen established a singular variant of patriarchal but sufficiently enlightened absolutism . He developed mines and industry and nationalised many branches of Transylvania ' s foreign trade . His agents bought up many products at fixed prices and sold them abroad at a profit , almost doubling his revenues . He built himself a grand new palace in his capital , Gyulafehérvár ( today Alba Iulia ) , kept a sumptuous court , composed hymns , and patronised the arts and learning , especially in connection with his own Calvinist faith . He founded an academy to which he invited any pastor and teacher from Royal Hungary ; sent students abroad to the Protestant universities of England , the Low Countries , and the Protestant principalities of Germany ; , conferred hereditary nobility on all Protestant pastors ; and forbade landlords to prevent their serfs from having their children schooled . Anti - Habsburg insurrection . Other parts of his revenue he devoted toward keeping an efficient standing army of mercenaries , with whose help he conducted an ambitious foreign policy . Keeping peace with the Ottoman Porte , he struck out to the north and west . There were several reasons for his anti - Habsburg interventions in neighbouring Royal Hungary ( 1619 – 1626 ) which took place during Central Europe ' s Thirty Years ' War : While Emperor Ferdinand II was occupied with the Bohemian rebellion of 1618 , Bethlen led his armies into Royal Hungary in August 1619 and occupied the town of Kassa ( Košice ) in September , where his Protestant supporters declared him " head " of Hungary and protector of the Protestants . He soon won over the entirety of Upper Hungary ( present - day Slovakia ) , even securing the capital of Royal Hungary , Pozsony ( Bratislava ) , in October , where the palatine even handed over the Crown of St Stephen to Bethlen . Bethlen ' s troops joined with the troops of the Czech and Moravian estates ( led by Count Jindrich Matyas Thurn ) , but they failed to conquer Vienna in November – Bethlen was forced to leave Austria after being attacked by George Druget and Polish mercenaries ( lisowczycy ) in Upper Hungary . Although he had conquered most of Royal Hungary , Bethlen was not averse to a peace , nor to a preliminary suspension of hostilities , and negotiations were opened at the conquered towns of Pressburg , Kassa and Besztercebánya ( Banská Bystrica ) . Initially , they led to nothing because Bethlen insisted on including the Czechs in the peace , but finally a truce was concluded in January 1620 under which Bethlen received 13 counties in the east of Royal Hungary . On 20 August 1620 the estates elected him King of Hungary at the Diet in Besztercebánya with the consent of the Ottomans and he wanted to reconcile with the Habsburgs and reunite Hungary . However , the war with the Habsburgs resumed in Royal Hungary and Lower Austria in September . The defeat of the Czech rebels by Ferdinand II ’ s troops at the Battle of White Mountain on 8 November 1620 ( to which Bethlen had sent 3 , 000 troops which arrived too late ) gave a new turn to Bethlen ’ s insurrection against the Habsburgs . Ferdinand II took a fearful revenge upon the Protestant nobility in Bohemia and reconquered Royal Hungary ( Pozsony reconquered in May 1621 , central part of the country with the mining towns in June 1621 ) . Because the Protestant nobles had not received the confiscated property of the Catholics on Bethlen ' s territory and thus rescinded their support for Bethlen , and because Bethlen was not directly supported by the Ottomans , Bethlen started peace negotiations . As a result , the Treaty of Nikolsburg was concluded on 31 December 1621 , under which Bethlen renounced the royal title on condition that Ferdinand confirmed the 1606 Peace of Vienna ( which had granted full liberty of worship to the Hungarian Protestants ) and engaged to summon a general diet within six months ) . The treaty granted full liberty of worship to the Protestants of Hungarian Transylvania and agreed on the summoning of a general diet within six months . In addition , Bethlen secured the ( purely formal ) title of “ Imperial Prince “ ( of Hungarian Transylvania ) , seven counties around the Upper Tisza River and the fortresses of Tokaj , Munkács , and Ecsed , and a duchy in Silesia . Subsequently Bethlen twice ( 1623 – 1624 and 1626 ) launched further campaigns against Ferdinand to the territory of Upper Hungary ( present - day Slovakia ) , this time as a direct ally of the anti - Habsburg Protestant powers . The first war was concluded by the 1624 Peace of Vienna , the second by the 1626 Peace of Pressburg - both confirmed the 1621 Peace of Nikolsburg . After the second of these campaigns , Bethlen attempted a rapprochement with the court of Vienna on the basis of an alliance against the Turks and his own marriage with an archduchess of Austria , but Ferdinand rejected his overtures . Bethlen was obliged to renounce his anti - Turkish projects , which had always remained a goal of his . Accordingly , on his return from Vienna he wedded Catherine of Brandenburg , the daughter of John Sigismund , Elector of Brandenburg , and still more closely allied himself with the Protestant powers , including his brother - in - law Gustavus Adolphus of Sweden , who , he hoped , would aid him in obtaining the Polish crown . Bethlen died on 15 November 1629 before he could accomplish any of his great designs to unite Transylvania and Hungary , having previously secured the election of his wife Catherine as princess . His first wife , Zsuzsanna Károlyi , died in 1622 . Other achievements . A zealous Calvinist who boasted he had read the Bible twenty - five times , he helped the Jesuit György Káldy translating and printing his version of the Scriptures . He was in communication all his life with the leading contemporary statesmen , so that his correspondence is an important historical document . He also composed hymns and employed the composer Johannes Thesselius as " kapellmeister " from 1625 .