[7] Vladislaus's brother, King Sigismund Jagiellon of Poland, came to Hungary to mediate between the royal family and the Zápolyas in late June.

[8] Emperor Maximilian had already in September declared war on Hungary, because he wanted to protect his claim (acknowledged in the 1491 Peace of Pressburg) to succeed Vladislaus.

[6] Hedwig of Cieszyn wanted to persuade Vladislaus II, King of Hungary and Bohemia, to marry his only child, Anne, to John.

On 13 October, the Diet, prompted by Zápolya,[12] passed a bill which prohibited the election of a foreigner as king if Vladislaus died without male issue.

[20] Vladislaus's brother, Polish king Sigismund I the Old, married John's younger sister, Barbara Zápolya in early 1512.

[22] After returning to Transylvania, he crushed a revolt in Hermannstadt (now Sibiu, Romania) and forced the townspeople to pay an extraordinary tax.

[29][28] In October, the Diet deprived the peasants of the right to free movement and obliged them to work on their lords' lands without remuneration one day in every week.

[30] Supporters of Zápolya were appointed to the royal council, becoming a majority, and his friend, Gregory Frankopan, Archbishop of Kalocsa, was made chancellor.

[31] Zápolya, Stephen Báthory, Emeric Török, and Michael Paksy joined forces to laid siege to Žrnov, the Ottoman fortress near Nándorfehérvár (now Belgrade, Serbia) in April 1515.

[31] In 1526, the Ottoman Empire crushed the Hungarian royal army in the Battle of Mohács and killed King Louis II.

The last three months of the year were marked by a power vacuum; political authority was in a state of collapse, yet the victors chose not to impose their rule.

The other was Archduke Ferdinand of Austria, the late king's brother-in-law and brother of Holy Roman Emperor Charles V, who claimed Hungary for the House of Habsburg.

The majority of Hungary's untitled lesser nobility (the gentry) backed Zápolya, who for fifteen years had been playing a leading role in Hungarian political life.

The likelihood of assistance was further reduced by the conflict of Ferdinand's older brother, Emperor Charles V, and King Francis I of France that once again flared into open war in the summer of 1526.

This circumstance led the Voivode to discount the threat lurking behind the Habsburgs' candidacy: that Zápolya's Hungary would have to contend not only with the Ottomans, but also with an attack from the west.

On 10 November 1526, Zápolya had himself proclaimed king at the Diet at Székesfehérvár by the lesser nobles (gentry), and he was duly crowned the next day.

He drew on his vast private wealth, the unconditional support of the lesser nobility, and the assistance of some aristocrats to impose his policies in domestic affairs.

Europe's political balance underwent a major shift in the summer of 1527, when, in a somewhat unplanned operation, mercenary forces of the emperor occupied Rome and drove Pope Clement VII, one of France's principal allies, to capitulate.

The moment was well chosen, for John Zápolya's forces were tied up in the southern counties of Hungary, where Slavonic peasants, incited by Ferdinand, had rebelled; the revolt was led by the 'Black Man', Jovan Nenad.

[34] After Szapolyai received no assistance from European rulers to resolve the ongoing war conflict with Ferdinand (only empty promises), he had no choice but to send his envoy, Laszky Jeromos, to Istanbul to seek help.

This was an old method used by the Ottoman Empire, which had also been applied against Balkan states, such as Serbia, in the 14th and 15th centuries, where they were first compelled into dependency and then annexed in the following decades.

Sultan Suleiman the Magnificent accepted, and sent Ottoman armies to invade Austria (which included the Siege of Vienna), a war which lasted till 1533.

This allowed John to regain his position in Hungary in 1529, by the efforts of Frater George Martinuzzi, despite the association with the Ottomans which tainted him at the time.