According to the opinion of the Hungarian historian, Miklós Istvánffy (1538–1615), the Szapolyai (Zapolja) family is originated in Croatia. Istvánffy says in his book -
Historiarum de rebus Ungaricis - that in Slavonia near
Csázma (Čazma) was Szapolya village. Later the the Szapolyais became counts of Szepes, and
János Szapolyai (Ivan Zapolja, 1487-1540), voivod of Transylvania in 1526 came to the throne of Hungary and Croatia as John I.
King John's son
John Sigismund (János Zsigmond, 1540-1571), elected king of Hungary and Croatia, prince of Transylvania, was a very intelligent and educated ruler. In the court of John Sigismund, the Italian Anti-trinitarian refugee Giorgio Blandrata found a congenial religious environment and under the influence of Blandrata and Ferenc Dávid the young John Sigismund became the first Unitarian king in the world.
In 1568 the famous Decret of Torda was issued. King John Sigismund did not decree that everyone become Unitarian, though many citizens did so, but issued an edict of religious tolerance.