Treaty of Constantinople (1533)
During the Battle of Mohács in 1526 the king of Hungary, Louis II, had died without an heir to throne. But the Ottoman Empire did not annex Hungary after the war and the Hungarian throne was left vacant for several months. Two claimants emerged: Ferdinand I, the archduke of Austria; and János Szapolyai, the voivode (governor) of Transylvania (Turkish: Erdel, western part of modern Romania). Although Szapolyai was backed by a majority of the Hungarian elite, Ferdinand nevertheless declared himself the legal king of Hungary with the support of his older brother Charles V, Holy Roman Emperor. The Ottoman Empire, however, backed Szapolyai and Ottoman Emperor Suleyman I mounted a threat against Austria in two military campaigns (of 1529 and 1532). Ferdinand saw that it was impossible to establish his rule in Hungary.
Meanwhile the shah of Safavid Persia, Tahmasp I, became active in the eastern borders of the Ottoman Empire. Suleyman decided to concentrate his activities in the east, giving up his pursuit of hostilities in the west, and the treaty was signed.
The terms of the treaty were as follows:
- Ferdinand withdrew his assertions on Hungary (save a small territory in the west of Hungary) 
- Szapolyai was legitimized as the King of Hungary under Ottoman suzerainty.
- Austria agreed to pay annual tributes of 30,000 guldens.
- Ferdinand was to be considered as the King of Germany, and Charles V as the King of Spain, and they were equal to the Grand Vizier of Ottoman Empire. Moreover, they were banned to count anyone as 'Emperor' except the Ottoman Emperor.
Szapolyai didn't have a son and according to treaty of Nagyvárad signed in 1538, Ferdinand was the heir to throne. But after the treaty, Szapolyai's wife gave birth to a son. In 1540, when Szapolyai died of natural causes, Ferdinand reclaimed the throne, and the war was renewed. This time, Suleyman reversed his policy of allowing Hungary to persist as a vassal kingdom, and annexed most of Hungary in his two campaigns in 1541 and 1543. Szapolyai’s infant son was transferred to Transylvania, his father’s former principality.
References and notes
- Prof.Dr Yaşar Yücel-Prof.Dr Ali Sevim:Türkiye tarihi II, AKDTYK Yayınları, İstanbul,1990 pp 268-274
- Lord Kinross :The Ottoman centuries, (Trans.Meral Gaspıralı) Altın Kitaplar, İstanbul, 2008, ISBN 978-975-21-0955-1, p.193
- Nicolae Jorga: Gescchiste des Osmanichen, (trans: Nilüfer Epçeli) Yeditepe Yayınları, 2009, ISBN 975-6840-19-X volII,p.350-351
- Encyclopaedia Britannica, Expo 70 ed., Vol 9, p 177