- Oct 2011
No, it did not. Croatia was in personal union with Hungary before then. Decision had to be made independently by Croatia; Hungary could not have forced Croatia to enter union with Habsburgs in any way short of outright military conquest.Ferdinand was elected to king of Hungary by the higher aristocracy (the magnates or barons) and the Hungarian Catholic clergy in a rump Diet in Pozsony on 17 December 1526.
Croatian parliament of Cetin maybe just affirmed the Hungarian parliament's decision on 1 of January, 1527
Technically only Austrian part of the Monarchy was part of Holy Roman Empire, but Habsburgs had been Holy Roman Emperors for centuries at that point, so I tend to equate the two when it comes to Austria.Sorry, but I can not found any info about the vassalage, maybe it exist only in your own imagination. Sure that Hungary was never been part of the HRE, there were such attempts, but the Hungarian nobility resisted against the very idea.