Editors. "The infant John Sigismund Zápolya succeeds as King of Hungary". The Literary Encyclopedia. First published 01 November 2010
[http://www.litencyc.com/php/stopics.php?rec=true&UID=14642, accessed 17 April 2014.]
King John Zápolya of Hungary dies, and his infant son John Sigismund Zápolya takes the throne. This goes against the treaty of 1538, which promised the succession to Archduke Ferdinand of Austria and Bohemia. As a result, Ferdinand sends troops into Hungary to claim the whole country and lays siege to the capital city of Buda, provoking the intervention of the Ottoman Sultan Suleiman I.