John Sigismund Zápolya in the context of "Tisza"

The Kingdom of Hungary between 1526 and 1867 existed as a state outside the Holy Roman Empire, but part of the lands of the Habsburg monarchy that became the Austrian Empire in 1804. After the Battle of Mohács in 1526, the country was ruled by two crowned kings (John I and Ferdinand I). Initially, the exact territory under Habsburg rule was disputed because both rulers claimed the whole kingdom. This unsettled period lasted until 1570 when John Sigismund Zápolya (John II) abdicated as King of Hungary in Emperor Maximilian II's favor.

In the early stages, the lands that were ruled by the Habsburg Hungarian kings were regarded as both the "Kingdom of Hungary" and "Royal Hungary". Royal Hungary was the symbol of the continuity of formal law after the Ottoman occupation, because it could preserve its legal traditions, but in general, it was de facto a Habsburg province. The Hungarian nobility forced Vienna to admit that Hungary was a special unit of the Habsburg lands and had to be ruled in conformity with its own special laws. However, Hungarian historiography positioned Transylvania in a direct continuity with the medieval Kingdom of Hungary in pursuance of the advancement of Hungarian interests.

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 Holy Crown of Hungary (Hungarian: Szent Korona [ˈsɛnt ˈkoronɒ], Latin: Sacra Corona), also known as the Crown of Saint Stephen, named in honour of Saint Stephen I of Hungary, was the coronation crown used by the Kingdom of Hungary for most of its existence; kings were crowned with it since the twelfth century. The Crown symbolized the King's authority over the Lands of the Hungarian Crown, and it was a key mark of legitimacy. Through the history of Hungary, more than fifty kings were crowned with it, with the last being Charles IV in 1916. The only kings not crowned were Wladyslaw I, John Sigismund Zápolya, and Joseph II.

The enamels on the crown are mainly or entirely Byzantine work, presumed to have been made in Constantinople in the 1070s. The crown was presented by the Byzantine Emperor Michael VII Doukas to the King Géza I of Hungary; both are depicted and named in the Greek language on enamel plaques in the lower crown. However, in popular tradition the Holy Crown was thought to be older and of Papal provenance, dating to the time of the first King Stephen I of Hungary crowned 1000/1001. It is one of two known Byzantine crowns to survive, the other being the slightly earlier Monomachus Crown in the Hungarian National Museum, which may have had another function. The Holy Crown has probably been remodelled using elements of different origins. The date assigned to the present configuration of the Holy Crown is most commonly put around the late 12th century. The Hungarian coronation regalia consists of the Holy Crown, the sceptre, the orb, and the mantle. The orb has the coat of arms of Charles I (1310–1342).

The Prince of Transylvania (Hungarian: erdélyi fejedelem, German: Fürst von Siebenbürgen, Latin: princeps Transsylvaniae, Romanian: principele Transilvaniei) was the head of state of the Principality of Transylvania from the late-16th century until the mid-18th century. John Sigismund Zápolya was the first to adopt the title in 1570, but its use became stable only from 1576.

Isabella Jagiellon (Hungarian: Izabella királyné; Polish: Izabela Jagiellonka; Lithuanian: Izabelė Jogailaitė; 18 January 1519 – 15 September 1559) was a princess of the Kingdom of Poland and of the Grand Duchy of Lithuania, and later also the Queen consort of Hungary. She was the oldest child of Sigismund I the Old, King of Poland and Grand Duke of Lithuania, and his Italian wife Bona Sforza.

In 1539, she married John Zápolya, Voivode of Transylvania and King of Hungary. At the time Hungary was contested between Ferdinand of Austria who wanted to add it to the Habsburg domains (see Royal Hungary), local nobles who wanted to keep Hungary independent (see Eastern Hungarian Kingdom), and Sultan Suleiman the Magnificent who saw it as a vassal state of the Ottoman Empire (see also Little War in Hungary). While Isabella's marriage lasted only a year and a half, it did produce a male heir – John Sigismund Zápolya born just two weeks before his father's death in July 1540.

George Martinuzzi, O.S.P.P.E. (born Juraj Utješenović, also known as György Martinuzzi, Brother György, Georg Utiessenovicz-Martinuzzi or György Fráter, Hungarian: Fráter György; 1482 – 16 December 1551), was a Croatian nobleman, Pauline monk and Hungarian statesman who supported King John Zápolya and his son, King John Sigismund Zápolya. He was Bishop of Nagyvárad (now Oradea), Archbishop of Esztergom and a cardinal.

The Treaty of Speyer, signed at the Diet of Speyer in 1570, was a peace agreement between the two Hungarian Kingdoms, Royal Hungary led by Maximilian II, and the Eastern Hungarian Kingdom, ruled by John Sigismund Zápolya, which lead to the establishment of the Principality of Transylvania.