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.

[2] The Habsburgs tried several times to unite all Hungary under their rule, but the Ottoman Empire prevented that by supporting the Eastern Hungarian Kingdom.

Ferdinand of Austria, younger brother of Emperor Charles V, claimed the crown by right of his marriage to Louis' sister Anne.

[5] For much of John II's reign, Eastern Hungary was governed by his mother, Isabella, with Bishop George Martinuzzi as regent.

Martinuzzi called on Suleiman, who expelled Ferdinand, but took most of central Hungary under direct Ottoman rule as Budin Province.

During the 1540s, the Eastern Hungarian Kingdom included the counties of Máramaros, Szabolcs, Szatmár, Közép-Szolnok, Bihar, Külső-Szolnok, Békés, Csongrád, Arad, Csanád, and the Temesköz.

Zemplén, Borsod, and Abaúj Counties with their undefined borders were ruled by the Balassa, Losonci, Bebek, and Drugeth families, but they possessed considerable autonomy.

[6] The army campaigns of 1543–44 left only one secure road link to Royal Hungary, along the Vág valley, and this further decreased Habsburg support in the kingdom.

[6] In August 1544, commissioners from the central parts of the medieval Hungarian kingdom as counties along the Tisza river participated as equals in the Transylvanian Diet at Torda.

[6] The chancellery and the high court at Buda disappeared during the political chaos of 1540-41 and Transylvania could not be administered by the central organs of the Hungarian Kingdom anymore.

[6] King John's supporters usually had no roots within the new confines of the country, however their relatives were found among the senior officials and courtiers in large numbers.

John II again renounced his claim as king of Hungary in favor of Maximilian, thus ending the Eastern Hungarian Kingdom.

Despite John Sigismund's profession of vassalage to Maximilian, the princes of Transylvania ruled with near complete autonomy, and often paid tribute to the Ottoman Empire.