The ambitious monarch, having thus for succeeded, looked with a covetous eye towards Transylvania.  That majestic province, on the eastern borders of Hungary, being three times the size of Massachusetts, and containing a population of about two millions, would prove a splendid addition to the Hungarian kingdom.  While Matthias was secretly encouraging what in modern times and republican parlance is called a filibustering expedition, for the sake of annexing Transylvania to the area of Hungary, a new object of ambition, and one still more alluring, opened before him.

The Protestants in Bohemia were quite excited when they heard of the great privileges which their brethren in Hungary, and in the Austrian provinces had extorted from Matthias.  This rendered them more restless under the intolerable burdens imposed upon them.  Soon after the armies of Matthias had withdrawn from Bohemia, Rhodolph, according to his promise, summoned a diet to deliberate upon the state of affairs.  The Protestants, who despised Rhodolph, attended the diet, resolved to demand reform, and, if necessary, to seek it by force of arms.  They at once assumed a bold front, and refused to discuss any civil affairs whatever, until the freedom of religious worship, which they had enjoyed under Maximilian, was restored to them.  But Rhodolph, infatuated, and under the baleful influence of the Jesuits, refused to listen to their appeal.

Matthias, informed of this state of affairs, saw that there was a fine opportunity for him to place himself at the head of the Protestants, who constituted not only a majority in Bohemia, but were also a majority in the diet.  He therefore sent his emissaries among them to encourage them with assurances of his sympathy and aid.  The diet which Rhodolph had summoned, separated without coming to other result than rousing thoroughly the spirit of the Protestants.  They boldly called another diet to meet in May, in the city of Prague itself, under the very shadow of the palace of Rhodolph, and sent deputies to Matthias, and to the Protestant princes generally of the German empire, soliciting their support.  Rhodolph issued a proclamation forbidding them to meet.  Regardless of this injunction they met, at the appointed time and place, opened the meeting with imposing ceremonies, and made quiet preparation to repel force with force.  These preparations were so effectually made that upon an alarm being given that the troops of Rhodolph were approaching to disperse the assembly, in less than an hour twelve hundred mounted knights and more than ten thousand foot soldiers surrounded their hall as a guard.