Complex sentence: The throne of Hungary became the subject of a dynastic dispute between Ferdinand and John Zápolya, from Transylvania, a supporter of King Louis II whom Suleiman had promised to make the ruler of all Hungary.
Split into simpler sentences: The throne of Hungary became the subject of a dynastic dispute between Ferdinand and John Zápolya from Transylvania. Zápolya was a supporter of King Louis II whom Suleiman had promised to make the ruler of all Hungary.