John paid homage to Suleiman at Mohács in 1529 to secure Ottoman support against Ferdinand. However, neither John nor Ferdinand could win control of the whole country during the next years. To conclude the civil war, the two kings' envoys signed the Treaty of Várad on 24February 1538, which confirmed both kings' right to retain the lands that they held. John, who was childless, also acknowledged Ferdinand's right to take control of his realm (the central and eastern part of the Kingdom of Hungary) after his death. John also stipulated, if he fathered a son, his son would inherit his ancestral domains. Ferdinand, however, proved unable to protect John's realm against an Ottoman invasion. At age 52 John married Isabella Jagiellon, the 22-year-old daughter of Sigismund I the Old, King of Poland, on 2March 1539. The humanist scholars Paolo Giovio and Antun Vrančić emphasized that Isabella was one of the most educated women of their age.