Treaty of Speyer (1570)
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 Maximiliam II, and the Eastern Hungarian Kingdom, ruled by John Sigismund Zápolya. John Sigismund abdicated as King of Hungary, however Maximiliam II recognized John Sigismund's authority as "Prince of Transylvania" and in return John Sigismund accepted Maximiliam II as King of Hungary with vassalage over his principality.
John Sigismund became princeps Transsylvaniae et partium regni Hungariae dominus – Prince of Transylvania and of a part of the Kingdom of Hungary. According to the treaty Principality of Transylvania continued to be part of the Kingdom of Hungary in the sense of public law.
- Andrew Pettegree, The Reformation World, Routledge, 2000, p. 192
- István Keul, Early modern religious communities in East-Central Europe: ethnic diversity, denominational plurality, and corporative politics in the principality of Transylvania (1526–1691), BRILL, 2009, p. 61
- Anthony Endrey, The Holy Crown of Hungary, Hungarian Institute, 1978, p. 70