Principality of Transylvania (1570–1711) in the context of "Kingdom of Hungary"

The Eastern Hungarian Kingdom (Hungarian: keleti Magyar Királyság [ˈkɛlɛti ˈmɒɟɒr ˈkiraːjʃaːg]) is a modern term coined by some historians to designate the realm of John Zápolya and his son John Sigismund Zápolya, who contested the claims of the House of Habsburg to rule the Kingdom of Hungary from 1526 to 1570. The Zápolyas ruled over an eastern part of Hungary, and the Habsburg kings (Ferdinand and Maximilian) ruled the west. The Habsburgs tried several times to unite all Hungary under their rule, but the Ottoman Empire prevented that by supporting the Eastern Hungarian Kingdom.

The exact extent of the Zápolya realm was never settled because both the Habsburgs and the Zápolyas claimed the whole kingdom. A temporary territorial division was made in the Treaty of Nagyvárad in 1538. The Eastern Hungarian Kingdom is considered the predecessor of the Principality of Transylvania (1570–1711), which was established by the Treaty of Speyer.

The Principality of Transylvania, from 1765 the Grand Principality of Transylvania, was a realm of the Hungarian Crown ruled by the Habsburg and Habsburg-Lorraine monarchs of the Habsburg monarchy (later Austrian Empire) and governed by mostly Hungarians. After the Ottomans were ousted from most of the territories of medieval Kingdom of Hungary, and after the failure of Rákóczi's War of Independence (1703–1711), the Habsburg dynasty claimed the former territories of the Principality of Transylvania under the capacity of their title of "King of Hungary". During the Hungarian Revolution of 1848, the Hungarian government proclaimed union with Transylvania in the April Laws of 1848 (after the Transylvanian Diet's confirmation on 30 May and the king's approval on 10 June for Transylvania to become once again an integral part of Hungary). After the failure of the revolution, the March Constitution of Austria decreed that the Principality of Transylvania be a separate crown land entirely independent of Hungary. In 1867, as a result of the Austro-Hungarian Compromise, the principality was reunited with Hungary proper.

In Romanian historiography, the Great Union (Romanian: Marea Unire) or Great Union of 1918 (Marea Unire din 1918) was the series of political unifications the Kingdom of Romania had with several of the Romanian historical regions, starting with Bessarabia on 27 March 1918, continuing with Bukovina on 28 November 1918 and finalizing with Transylvania (on its broad meaning) on 1 December 1918 with the declaration of the union of this region with Romania during an assembly at the city of Alba Iulia. Romanians also consider several other events as preludes to the Great Union, such as the unification of Moldavia and Wallachia (also known as the Little Union, Mica Unire) in 1859 or the independence of the country and the annexation of Northern Dobruja in 1878, and also the occupation of Transylvania and Moldavia by the Prince of Wallachia, Michael the Brave, in 1600.

Today, the Great Union has an important meaning in Romania, and it is commemorated in the Great Union Day, the national day of the country, every 1 December. The centenary of the Great Union on 1 December 2018 was widely celebrated in Romania, with military parades at cities like Alba Iulia and Bucharest to which many people (up to 550,000, 100,000 of them in Alba Iulia alone), including the President of Romania Klaus Iohannis, attended. The centenary was also celebrated in Moldova, where more than 100 localities and 3 districts declared unification with Romania.

Michael the Brave (Romanian: Mihai Viteazul [miˈhaj viˈte̯azul] or Mihai Bravu [ˈbravu]; 1558 – 9 August 1601), born as Mihai Pătrașcu, was the Prince of Wallachia (as Michael II, 1593–1601), Prince of Moldavia (1600) and de facto ruler of Transylvania (1599–1600). He is considered one of Romania's greatest national heroes. Since the 19th century, Michael the Brave has been regarded by Romanian nationalists as a symbol of Romanian unity, as his reign marked the first time in history all principalities inhabited by Romanians were under the same ruler.

His rule over Wallachia began in the autumn of 1593. Two years later, war with the Ottomans began, a conflict in which the Prince fought the Battle of Călugăreni, resulting in a victory against an army nearly three times the size of the army of Michael the Brave, considered one of the most important battles of his reign. Although the Wallachians emerged victorious from the battle, Michael was forced to retreat with his troops and wait for aid from his allies, Prince Sigismund Báthory of Transylvania and Holy Roman Emperor Rudolf II. The war continued until a peace finally emerged in January 1597, but this lasted for only a year and a half. Peace was again reached in late 1599, when Michael was unable to continue the war due to lack of support from his allies. In 1599, Michael won the Battle of Șelimbăr against Andrew Báthory and soon entered Gyulafehérvár (today Alba Iulia, Romania), becoming the imperial governor (i.e. de facto ruler) of Transylvania, under Habsburg suzerainty. A few months later, Michael's troops invaded Moldavia and reached its capital, Iași. The Moldavian leader Ieremia Movilă fled to Poland and Michael was declared Prince of Moldavia. During this period, Michael the Brave changed his seal to represent his personal union of Wallachia, Moldavia, and Transylvania.

Alba Iulia (Romanian pronunciation: [ˌalba ˈjuli.a] ; German: Karlsburg or Carlsburg, formerly Weißenburg [ˈvaɪsn̩bʊʁk] ; Hungarian: Gyulafehérvár [ˈɟulɒfɛɦeːrvaːr]; Latin: Apulum) is a city that serves as the seat of Alba County in the west-central part of Romania. Located on the river Mureș in the historical region of Transylvania, it has a population of 64,227 (as of 2021).

During ancient times, the site was the location of the Roman camp Apulum. Since the High Middle Ages, the city has been the seat of Transylvania's Roman Catholic diocese. Between 1526 and 1570 it was the capital of the Eastern Hungarian Kingdom from which the Principality of Transylvania emerged by the Treaty of Speyer in 1570 and it was the capital of the Principality of Transylvania until 1711. At one point it also was a center of the Eastern Orthodox Metropolitan of Transylvania with suffragan to Vad diocese. On 1 December 1918, the Union of Transylvania with Romania was declared in Alba Iulia, and Romania's King Ferdinand I and, in 1922 Queen Marie were crowned in the Alba Iulia Orthodox Cathedral.

The Bocskai uprising, known in Hungary as Bocskai's War of Independence (Hungarian: Bocskai szabadságharc, Bocskai-felkelés) was a revolt which took place in Hungary, Transylvania and modern Slovakia during the Long Turkish War (between 1604 and 1606) against Emperor Rudolf II. The rebel leader was Stephen Bocskai, a Protestant Hungarian nobleman. The Ottoman wars had burdened the Kingdom of Hungary for years, causing famine and disease, and the armies of the Christian states had been weakened by losses to Ottoman and Tatar forces.

Rudolf II persecuted the Protestants, and the wealthy Hungarian noblemen were falsely accused of treason. Bocskai organized the revolt and persuaded the Hungarian military Hajduks to join, defeating the imperial forces and foreign mercenaries. The Hungarian nobility, soldiers and peasants (including the minorities) joined Bocskai's Hajduk army. Although he was supported by the Ottoman Empire, the Crimean Khanate, Moldavia, Transylvania, he prevented an Ottoman siege of Vienna. Bocskai was declared Prince of Transylvania and Hungary, but recognized that total Hungarian independence was impossible against the Habsburg monarchy and the Ottoman Empire. He blazed a political trail for his supporters: the preservation of an independent Transylvania, a potential base for the unification of Hungary. Based on the terms of the Treaty of Vienna in 1606, all constitutional and religious rights and privileges were granted to the Hungarians in both the Principality of Transylvania and Royal Hungary. The treaty also recognized Bocskai as the Prince of Transylvania and guaranteed the right of Transylvanians to elect their own independent princes in the future.