had attracted many from the Lutheran ranks by the greater clarity of its doctrine and the greater cohesion of its organization. Now, when the struggle was over, Protestantism was divided within itself. Calvinist States lay mingled with Lutheran principalities, and their rulers occupied themselves with making leagues to extend their own particular shade of thought rather than in uniting against the common foe. Finally, the Peace of Augsburg contained within itself the seeds of fresh warfare. The term Protestantism was considered to include only those who had signed the Confession of Augsburg; toleration for adherents of the Lutheran faith in Catholic lands was refused; and no satisfactory settlement was made of the crucial question of the secularized territories, the lands of the bishoprics which had been converted to Protestantism.
In all these circumstances Protestantism was bound to suffer when a vigorous attack was launched upon it. Between 1555 and 1618 there was widespread reversion to Catholicism, especially in the ecclesiastical territories; it was the fear that the forces of the Church would soon be everywhere triumphant that at last drew the Protestant princes together in some sort of unity. With Protestantism once more in fighting mood, war in Germany was inevitable. Progress towards an internal struggle was eagerly watched by France, which, under the leadership of Henry IV, was rapidly regaining her internal prosperity and beginning to envisage a European hegemony. The power of the Habsburgs in Spain and Austria was an obstacle to this; the weakening of the imperial power by an internecine struggle in Germany was to France's advantage. Sweden, too, would profit by German weakness in her plans for the domination of the Baltic. The actual cause of the outbreak of the Thirty Years' War, the Bohemian succession, was but a minor matter; the effective causes must be looked for in the Counter Reformation, the determination of the princes to render impotent the imperial power in Germany, and the ambitions of European rulers.
The bibliographical material for such a long period is too extensive for any adequate bibliography to be given. The following list is only intended to suggest some German authorities which cover the whole period, and a few outstanding English works.
Deutsche Geschichte im Überblick, ed. Peter Rassow. Stuttgart, 1952-53
Haller, Johannes. Epochs of German History. London, 1930
Monumenta Germaniae historica, ed. Pertz. 1826
(The standard collection of chronicles, laws, letters, and miscellaneous documents between 500 and 1500 A.D. Includes such writings as Einhard Vita Karoli Magni, and Otto of Freising's Gesta [Frederici imperatoris].)