Principality of Transylvania ( 1570 – 1711 ) The Principality of Transylvania was a semi - independent state , ruled primarily by Hungarian princes . Its territory , in addition to the traditional Transylvanian lands , also included eastern regions of Hungary , the so - called " Partium " . The establishment of the principality was connected with Treaty of Speyer . However Stephen Báthory ' s status as king of Poland also helped to phase in the name " Principality of Transylvania " . It was usually under the suzerainty of the Ottoman Empire , however the principality often had dual vassalage ( Ottoman Turkish sultans and the Habsburg Hungarian kings ) in the 16th and 17th centuries . The polity was a symbol of the survival of Hungarian statehood . All traditional Hungarian law remained to be followed scrupulously in the principality , furthermore the state was imbued with a preponderantly Protestant feature . After the unsettled period of Rákóczi ' s War of Independence , it became part of the Habsburg Monarchy . Eastern Hungarian Kingdom and Zápolya family . On 29 August 1526 , the army of Sultan Suleiman of the Ottoman Empire inflicted a decisive defeat on the Hungarian forces at Mohács . John Zápolya was en route to the battlefield with his sizable army but did not participate in the battle for unknown reasons . The youthful King Louis II of Hungary and Bohemia fell in battle , as did many of his soldiers . As Zápolya was elected king of Hungary , Ferdinand from the House of Habsburg also claimed the throne of Hungary . In the ensuing struggle John Zápolya received the support of Sultan Suleiman I , who after his death in 1540 occupied Buda and central Hungary in 1541 under the pretext of protecting Zápolya ' s son , John II . Hungary was now divided into three sections : the West and north Royal Hungary , Ottoman Hungary , and the Eastern Hungarian Kingdom under Ottoman suzerainty , which later became the Principality of Transylvania where Austrian and Turkish influences vied for supremacy for nearly two centuries . The Hungarian magnates of Transylvania resorted to policy of duplicity in order to preserve independence . Transylvania was administrated by Isabella , John Sigismund ' s mother from 1541 to 1551 , when it fell for 5 years ( 1551 – 1556 ) under Habsburg rule . Zapolya House gained again the control of Transylvania in 1556 , when the Diet of Szászsebes elected Sigismund as prince of Transylvania . Transylvania was now beyond the reach of Catholic religious authority , allowing Lutheran and Calvinist preaching to flourish . In 1563 , Giorgio Blandrata was appointed as court physician , and his radical religious ideas increasingly influenced both the young king John II and the Calvinist bishop Francis David , eventually converting both to the Anti - Trinitarian ( Unitarian ) creed . In a formal public disputation , Francis David prevailed over the Calvinist Peter Melius ; resulting in 1568 in the formal adoption of individual freedom of religious expression under the Edict of Turda ( the first such legal guarantee of religious freedom in Christian Europe , however only for Lutherans , Calvinists , Unitarians and of course Catholics , with the Orthodox Christian confession being explicitly banned ) . Principality of Transylvania . Principality of Transylvania was established in 1570 when John II renounced his claim as King of Hungary in the Treaty of Speyer ( ratified in 1571 ) , however he became a Transylvanian prince . The treaty also recognized that Principality of Transylvania belonged to the Kingdom of Hungary in the sense of public law . The Báthory family , which came to power on the death of John II in 1571 , ruled Transylvania as princes under the Ottomans , and briefly under Habsburg suzerainty , until 1602 . Their rise to power marked the beginning of the Principality of Transylvania as a semi - independent state . The younger Stephen Báthory , the first powerful prince of independent Transylvania , a Hungarian Catholic who later became King under the name Stephen Bathory of Poland , undertook to maintain the religious liberty granted by the Edict of Turda , but interpreted this obligation in an increasingly restricted sense . The latter period of Báthory rule saw Transylvania under Sigismund Báthory - prince of the Holy Roman Empire - enter the Long War , which started as a Christian alliance against the Turks and became a four - sided conflict involving Transylvania , the Habsburgs , the Ottomans , and the voivode of Wallachia , Michael the Brave . After 1601 the Principality for a short time was under the rule of Rudolf I who initiated the Germanization of the population , and in order to reclaim the Principality for Catholicism the Counter Reformation . From 1604 to 1606 , the Hungarian nobleman Stephen Bocskay led a successful rebellion against Austrian rule . Bocskay was elected Prince of Transylvania on 5 April 1603 and prince of Hungary two months later . He achieved the Peace of Vienna in 1606 . By the Peace of Vienna , Bocskay obtained religious liberty and political autonomy , the restoration of all confiscated estates , the repeal of all " unrighteous " judgments , and a complete retroactive amnesty for all Hungarians in Royal Hungary , as well as his own recognition as independent sovereign prince of an enlarged Principality of Transylvania . By the Treaty of Vienna ( 1606 ) was guaranteed the right of Transylvanians to elect their own independent princes , but Georg Keglević , who was the Commander - in - chief , General , Vice - Ban of Croatia , Slavonia and Dalmatia , was since 1602 Baron in Transylvania . It was a very difficult and complicated peace treaty after a long war . Under Bocskay ' s successors Transylvania had its golden age , especially under the reigns of Gábor Bethlen and George I Rákóczi . Gábor Bethlen , who reigned from 1613 to 1629 , perpetually thwarted all efforts of the emperor to oppress or circumvent his subjects , and won reputation abroad by championing the Protestant cause . Three times he waged war on the emperor , twice he was proclaimed King of Hungary , and by the Peace of Nikolsburg ( December 31 , 1621 ) he obtained for the Protestants a confirmation of the Treaty of Vienna , and for himself seven additional counties in northern Hungary . Bethlen ' s successor , George I Rákóczi , was equally successful . His principal achievement was the Peace of Linz ( September 16 , 1645 ) , the last political triumph of Hungarian Protestantism , in which the emperor was forced to confirm again the articles of the Peace of Vienna . Gabriel Bethlen and George I Rákóczi also did much for education and culture , and their era has justly been called the golden era of Transylvania . They lavished money on the embellishment of their capital Alba Iulia , which became the main bulwark of Protestantism in Eastern Europe . During their reign Transylvania was also one of the few European countries where Roman Catholics , Calvinists , Lutherans , and Unitarians lived in mutual tolerance , all of them belonging to the officially accepted religions – " religiones recaepte " , while the Orthodox , however , were only tolerated . The fall of Nagyvárad ( 1660 ) marked the decline of the Principality of Transylvania with the Habsburg monarchs gaining increased control of this territory . Under Prince Kemeny , the diet of Transylvania proclaimed the secession of Transylvania from the Ottomans ( April 1661 ) and appealed for help to Vienna but a secret Habsburg - Ottoman agreement resulted in further increasing Habsburg influence . After the defeat of the Ottomans at the Battle of Vienna in 1683 , the Habsburgs gradually began to impose their rule on the formerly autonomous Transylvania . At the end of the 17th century , Transylvania was attached to the Habsburg controlled Hungary and subjected to the direct rule of the emperor ' s governors . From 1711 onward , Habsburg control over Transylvania was consolidated , and the princes of Transylvania were replaced with governors . Demographics . Until 1691 Transylvania was ruled by Unio Trium Nationum , the three state - constituting nations consisting of the Hungarian nobility , the Saxon urban settlers , and the Székely peasant - soldiers The coalition of the " Three Nations " retained its legal representative monopoly under the prince as before the split of the medieval Hungarian Kingdom . According to Dennis P . Hupchick , though there were occasional clashes between the Hungarian plainsmen and the Székely mountaineers , they were united under the patronymic " Magyars " and , with Saxon support , formed a common front against the predominantly Romanian peasantry . Official censuses with information on Transylvania ' s population have been conducted since the 18th century , but the ethnic composition was the subject of different modern estimations . Antun Vrančić ( Antonius Verancsics ) ( 1504 – 1573 ) wrote about the inhabitants of Transylvania and about the Romanians : " " the country is inhabited by three nations , Székelys , Hungarians , Saxons ; I would nevertheless add the Romanians , who , though they rather outnumber " [ the others ( ? ) ] " have no freedom , no aristocracy , no right of their own , besides a small number living in the Haţeg district , where they say Decebal ’ s capital was , and who , during the time of John Hunyadi , born there , were granted aristocratic status because they had always taken part in the struggle against the Turks . The other " [ Romanians ] " are all commoners , bondsmen to the Hungarians and having no place of their own , spread everywhere , throughout the country " " and lead " " a miserable life " " . According to Dennis P . Hupchick , Romanians were the majority population in the region during the rule of Stephen Báthory . In 1600 , according to George W . White , Romanians , who were primarily peasants , constituted more than 60 percent of the population . This theory is supported by Ion Ardeleanu , who states that the Romanian population represented " the overwhelming majority " in the age of Michael the Brave . By 1660 , according to Miklós Molnár , 955 , 000 people lived in the principality ( with Partium ) and the population consisted of 500 , 000 Hungarians ( including 250 , 000 Székelys ) , 280 , 000 Romanians , 90 , 000 Germans and 85 , 000 Serbians , Ukrainians and others and reached its end of century level . In ' s estimation , there were 250 , 000 Romanians , 150 , 000 Hungarians and 100 , 000 Saxons , in Transylvania , at the beginning of the 18th century . Károly Kocsis and Eszter Kocsisné Hodosi affirm that Hungarians were the most important ethnic group before the second half of the 17th century , when they were exceeded by Romanians . They assert the following structure of the population : in 1595 , out of a total population of 670 , 000 , 52 . 2 % were Hungarians , 28 . 4 % Romanians , 18 . 8 % Germans ; in 1720 , out of a total population of 806 , 221 , 49 . 6 % were Romanians , 37 . 2 % Hungarians , 12 . 4 % Germans .