From that moment the Protestant cause was lost; Saxony and Hesse-Darmstadt left the Union and joined Ferdinand.

Denmark, which had promised its assistance to the Protestants, was persuaded to remain quiet.

Sweden was engaged in a war with the Poles.
"The Protestant army was assembled at Ulm; the army of the League, under the order of Maximilian of Bavaria, was at Donauworth.

Maximilian worked upon the fears of the Protestant princes, who, frightened at the contest they had undertaken, agreed to a peace, by which they bound themselves to offer no aid to Frederick V.
"The Imperial forces then marched to Bohemia and attacked Frederick's army outside Prague, and in less than an hour completely defeated it.
Frederick escaped with his family to Holland.

Ferdinand then took steps to carry out his oath.