Ferdinand was even more vigorous than Maximilian in defence of his religion. On assuming the government of Styria he set to work to extirpate Protestantism, which had made considerable progress in the Austrian archduchies. Soon afterwards he was selected by the Habsburgs as the heir of the childless emperor Matthias, and on coming to Vienna after the death of that sovereign in March 1619 he found himself in the midst of hopeless confusion. The Bohemians refused to acknowledge him as their king and elected in his stead Frederick V., the elector palatine of the Rhine, a son-in-law of the English king James I., and the Hungarians and the Austrians were hardly less disaffected. As Ferdinand II., however, he succeeded in obtaining the imperial crown in August 1619, and from that time he was dominated by a fixed resolve to secure the triumph of his church throughout the Empire, a resolve which cost Germany the Thirty Years' War. The congress in Bohemia. He began with Bohemia. Although supported by Spain he could not obtain from this quarter an army sufficiently strong to crush the Bohemians, and for some time he remained powerless and inactive in Vienna. Then at the beginning of 1620 he came to terms with Maximilian of Bavaria, who, after carefully securing his own interests, placed the army of the League, commanded by the celebrated Tilly, at his disposal. Conditionally the Union promised assistance to Frederick, but he wasted several months and vaguely hoped that the English king would help him out of his embarrassments. Meanwhile Tilly advanced into Bohemia, and in November 1620 Frederick's army was utterly routed at the battle of the White Hill, near Prague, and the unfortunate elector had just time to escape from the kingdom he had rashly undertaken to govern. Ferdinand drove to the uttermost the advantages of his victory. The Union being destroyed and the Bohemian revolution crushed, attention was turned to the hereditary lands of the elector palatine. The Spanish troops and the army of the League invaded the Rhenish Palatinate, which was defended by Frederick's remaining adherents, Christian of Brunswick and Count Ernst von Mansfeld, but after several battles it passed completely into the possession of the imperialists. Having been placed under the imperial ban Frederick became an exile from his inheritance, and the electorate which he was declared to have forfeited was conferred on Maximilian. Danish interference in the war.