[This is taken from Rev. James A. MacCaffrey's History of the Catholic Church.]

The Religious Peace of Augsburg (1555) did not put an end to the struggle between the Catholics and Protestants in Germany. Feeling on both sides was too intense to permit either party to be satisfied with the arrangement or to accept it as a permanent definition of their respective rights. The German Catholics were indignant that a party that had sprung up so recently and that had done such injury to their Church and country, should be rewarded for heresy and disloyalty to the Emperor by such concessions. Nor was their indignation likely to be appeased by the manner in which Lutheran and Calvinist preachers caricatured and denounced the doctrines and practices of the Catholic world. Possibly it was, however, the clause of the Augsburg Peace known as the Ecclesiasticum Reservatum that gave rise to the most heated controversies, and played the greatest part in bringing about civil war. By this clause it was provided that in case any of the bishops and abbots passed over to the reformed religion they could not bring with them the ecclesiastical property attached to their office. The Lutherans, who had benefited so largely by such secessions from the Church in the past, objected to this clause at the Diet, and protested against the decision when their objections were overruled.

Having realized that the Emperor was unable or unwilling to prevent them they continued to act in open defiance of the Ecclesiasticum Reservatum. Where the territories of a Catholic bishop were situated in close proximity to the states of Protestant princes recourse was had to various devices to acquire the lands of the Church. Sometimes the bishop was induced to surrender them in return for a fixed grant or pension, sometimes the chapter was persuaded to elect as bishop some scion of a princely family, who was well-known to have leanings towards Protestantism, and in a few cases the bishops themselves solved the problem by seceding from the Catholic Church while continuing to administer the territories to which their episcopal office was their only title. In this way two archbishoprics and fourteen bishoprics, amongst them being such wealthy Sees as Magdeburg, Bremen, Brandenburg, and Osnabruck had passed into the hands of the Lutherans, and it required a very special effort to prevent two such important centers as Cologne and Aachen from meeting with a similar fate. Gebhard, Archbishop of Cologne, a man of scandalously immoral life, completed his infamous career by taking as his wife one who had been his concubine, announcing at the same time that he had gone over to Calvinism. The chapter of Cologne Cathedral backed by the people took steps to rid themselves of such a superior, and the chapter was supported warmly by both Pope and Emperor. Gebhard was obliged to escape to Strasburg in the cathedral of which he held a canonry, and where he succeeded in creating confusion. Two archbishops claimed the See of Strasburg, one loyal to the Catholic Church and one favoring Protestantism. This disgraceful contention went on for years, till at last the Protestant champion was induced to surrender on the payment of a large composition. The See of Aachen was seized by force in 1581, and was held for fifteen years, at the end of which the Protestants were obliged to abandon their claims.

Unfortunately for the Catholics the Emperors who succeeded Charles V. were not strong enough to deal with such a dangerous situation. Ferdinand I., sincere Catholic though he was, mindful of the terrible disasters brought upon his country by the religious wars, strove with all his might against their renewal. His successor Maximilian II. (1564-76) was so strongly inclined towards Protestantism that he made many concessions to the Protestants even in his own hereditary dominions. He invited distinguished Lutheran preachers to Vienna, conferred on Protestants influential positions at court, and gave permission for Protestant religious services at least to the nobles of Bohemia, Silesia, and Hungary. Several of the prince-bishops anxious to stand well with the Emperor attempted to introduce reforms in Catholic liturgy and Catholic practices without any reference to the Holy See. The alarming spread of Protestantism in Austria, Hungary, Bohemia, and Silesia, fostered as it was by the general policy of the Emperor, tended to make the position of the Catholic Church extremely insecure.

But fortunately at that time a strong Catholic reaction began to make itself felt. The reforming decrees of the Council of Trent did not fail to produce a decided improvement in the condition of the bishops and clergy. The new religious orders, particularly the Jesuits, had thrown themselves into the work of defending the Catholic position, and the colleges established by the Jesuits were turning out the younger generation of Catholics well-equipped for the struggle that lay before them. The catechisms which the Jesuit preachers scattered broadcast through the country, and the attention paid by them to the proper religious instruction of the people helped to remove the bad impressions produced by the misrepresentations of the Lutherans, and tended to arouse a strong, healthy, educated Catholic opinion in public life. Fortunately, too, at the time when the Emperors were a danger rather than a protection to the Church, the rules of Bavaria undertook boldly the defense of the old religion, and placed themselves at the head of the Catholic forces. Albert V. (1550-79) insisted on the promulgation of the decrees of the Council of Trent, and made an oath of loyalty to the Catholic Church an indispensable condition for office in his kingdom. He favored the Jesuits, encouraged their schools, and did everything in his power to strengthen Catholicism amongst his subjects. His policy was continued by Maximilian I. (1598-1651), who became the recognized leader of the advanced Catholic party in Germany.

This general unexpected revival, the success of which was shown by the fervor of the people, the unwillingness of the authorities to make any further concessions, and the determination of all parties to insist on the strict observance of the /Ecclesiasticum Reservatum/ filled the Protestants with such alarm that their princes began to insist on new guarantees. The Emperor, Rudolph II. (1576-1612), though, unlike his predecessor, a good Catholic, was a most incompetent ruler, devoting most of his time to alchemy and other such studies rather than to the work of government. He endeavored to solve the religious difficulties in Silesia and Bohemia by yielding to the Protestant demands (1609), but the interference of his brother Matthias led to new complications, and finally to Rudolph's abdication of the sovereignty of Bohemia (1611). Frederick IV. of the Palatinate was a strong Protestant, and was closely connected with the reforming party in England, Holland, and France. He thought he saw in the strife between the members of the House of Habsburg an opportunity of improving the position of Protestantism in the empire, of weakening the claims of the House of Habsburg to the imperial dignity, and possibly also of establishing himself as ruler of a united Germany.

An incident that took place at Donauworth, a city near the Rhine, helped him to realize his scheme of a great Protestant federation. This city was almost exclusively Catholic in 1555, but in one way or another the Protestants had succeeded in improving their position till at last only the abbey church remained to the Catholics. Here on the Feast of Corpus Christi in the year 1606 the customary procession of the Blessed Sacrament was attacked and dispersed, and the Catholics were treated with the greatest cruelty. When the matter was brought before the Emperor the city was placed under the ban of the empire, and Maximilian I. of Bavaria was entrusted with the task of carrying out the decree. He advanced with a strong army and captured the city. As the war indemnity could not be raised he retained possession of it, restoring to the Catholics everything they had lost. Frederick IV. made a strong appeal to the Protestant princes to show their resentment at such an act of aggression, pointing out to them that the fate of Donauworth would be the fate of all their territories unless they took united action. As a consequence when both parties met at the Diet of Regensburg (1608) the excitement was intense, and when the Emperor appealed to his princes for support against the Turks, the Protestants refused to lend their aid unless they received satisfactory explanations. The Catholics, encouraged by Maximilian, were equally unconciliatory, with the result that the Diet disbanded without having been able to arrive at an agreement.

A short time after the Diet most of the Protestant princes met at Ahausen and formed a confederation known as the Union (1608) at the head of which stood Frederick IV. of the Palatinate, while a little later a large number of the Catholic princes bound themselves together in the League and accepted Maximilian of Bavaria as their leader (1609). Thus Germany was divided once again into two hostile camps, and only a very trifling incident was required to plunge the country into another civil war. For a time it seemed as if the succession to the Duchy of Cleves was to be the issue that would lead to the catastrophe. Duke John William of Cleves had died without any direct heir, and as the religious issue was still undecided in his territory, the appointment of a successor was a matter of the greatest importance to both parties. The Emperor with the approval of the League nominated his brother Leopold as administrator, while the Union, having strengthened itself by an alliance with France, was prepared to take the field in favor of a Protestant. Henry IV. of France, anxious to turn the disputes that had broken out between the different members of the imperial family to the advantage of himself and his country, was actually on his way to take part in the campaign when he was assassinated. On his death both parties agreed to a temporary truce (1610), and thus the outbreak of the war was delayed for some time.

This delay was very fortunate for the Catholics in Germany. With such an Emperor as Rudolph pitted against a man like Henry IV. there could have been very little doubt about the issue. Even in his own territories Rudolph could not maintain his authority against his brother Matthias, in whose interest he was obliged to abdicate the throne of Bohemia (1611). On the death of Rudolph (1612) Matthias succeeded though not without considerable difficulty. As Emperor he showed himself much less favorable to the Protestants than he had been during the years when he was disputing with his brother, but, however well inclined, he was powerless to put an end to the division that existed or to control the policy of the League or the Union. The Duchy of Cleves was still an object of dispute. While the German Protestants invoked the aid of William of Orange and the Dutch Calvinists, the Catholics called in the forces of Spain. The Emperor could merely look on while his subjects allied themselves with foreigners to settle their own domestic troubles.

Meanwhile far more serious trouble was brewing in Bohemia, where the followers of Hus had blended with the disciples of Luther, and where in many centers there was a strong feeling against the Catholic Church. According to the concessions granted by Rudolph (1609), knights and free cities were at liberty to build Protestant churches, but a similar concession was not made to the subjects of Catholic lords. Regardless of or misinterpreting the terms of the concession, however, the Protestant tenants of the Archbishop of Prague and of the Abbot of Braunau built churches for their own use. The archbishop and abbot, considering themselves aggrieved, appealed to the imperial court. According to the decision of this court the church built on the lands of the archbishop was to be pulled down, and the other on the lands of the abbot was to be closed (1618). A deputation representing the Protestant party was appointed to interview the imperial representatives at Prague, and the reply to their remonstrances being regarded as unfavorable, the mob attacked the building, and hurled the councilors who were supposed to be responsible for it through the windows.

Under the direction of Count Thurn and some other Protestant nobles a provisional government was established in Bohemia, arrangements were made to organize an army, and as a beginning in the work of reform the Jesuits were expelled. Owing to the strong anti-German feeling of the populace the rebellion spread rapidly in Bohemia, and Count Mansfeld hastened to the relief of the insurgents with an army placed at his disposal by the /Union/. Most of the cities of Bohemia were captured by the rebels, and the whole of northern Austria stood in the gravest danger. At this critical moment the Emperor Matthias passed away, and was succeeded by Ferdinand II. (1619-37). The latter was a devoted Catholic, trained by the Jesuits, and had already done immense service to the Church by wiping out almost every trace of heresy in his hereditary dominions. That such a man should succeed to the imperial dignity at such a time was highly distasteful to the Protestants of Bohemia. It was not, therefore, to be wondered at that they refused to acknowledge him as king, and elected in his stead Frederick V. of the Palatinate (1619).

The situation looked exceedingly serious for Ferdinand II. On the one side he was being pressed hard by the Turks, and on the other he was beset so closely by the Bohemian rebels that even the very city of Vienna was in danger of falling into their hands. His opponent Frederick V. could rely upon the forces of the Union in the campaign, and besides, as the son-in-law of James I. of England and the nephew of Maurice of Orange the successful leader of the Dutch and the sworn ally of the French Huguenots, Frederick had little difficulty in persuading himself that at last Europe was to be freed from the domination of the House of Habsburg. He marched into Bohemia, and was crowned solemnly at Prague in 1619. But if Frederick could count upon support from many quarters so, too, could Ferdinand. Maximilian II. of Bavaria was active on his side, as were indeed the whole forces of the League. Saxony, too, which was devoted to Lutheranism and detested the Calvinist tendencies of Frederick, fearing that a victory for him might mean a victory for Calvinism, ranged itself under the banner of the Emperor. The Pope sent generous subsidies, as did also Spain. Finally, during the course of the campaign Ferdinand was fortunate in having the service of two of the ablest generals of their time, Tilly, who commanded the forces of the League, and Wallenstein who had charge of the imperial troops. Maximilian of Bavaria marched into Austria at the head of the army of the League and drove the rebels back into Bohemia, whither he followed them, and inflicted upon them a severe defeat in the battle of the White Mountain (1620). Frederick was obliged to save himself by flight after a reign of a few months. The leaders of the rebellion were arrested and put to death. In return for the services he had rendered Maximilian of Bavaria became ruler of the Palatinate, from which Frederick had been deposed. But though Frederick was defeated the struggle was by no means finished. The Count of Mansfeld, acting on behalf of the Union, espoused the cause of the Palgrave and was supported by an army led by Christian IV. of Denmark, Frederick's brother-in-law, who marched into Germany to the aid of his friends. James I. of England, though unwilling to dispatch an army, helped by grants of money. The war was renewed with great vigor, but the allies had little chance of success against two such experienced generals as Tilly and Wallenstein. Christian IV. suffered a terrible defeat at the Barenberg near Lutter (1626), and three years later he was forced to agree to the Peace of Lubeck (1629), by which he promised to withdraw from Germany and never again to mix himself up in its domestic affairs.

The forces of the Emperor and of the League were so victorious all along the line that the former felt himself strong enough to deal with the burning question of the ecclesiastical property that had been seized. In a short time he issued what is known as the Edict of Restitution (1629), by which he ordered that all property acquired by the Protestants contrary to the Ecclesiasticum Reservatum clause of the Peace of Augsburg (1555) should be restored. He commanded, besides, that the terms of the Peace of Passau-Augsburg should be strictly observed, allowed Catholic and Protestant princes the right of establishing their own religion in their own territories (Cuius regio illius religio), and permitted Protestant subjects of Catholic princes who felt their consciences aggrieved to emigrate if they wished to do so. About the justice of this decree there could be very little dispute, for it dealt only with the return of what had been acquired by open or veiled spoliation, but it may well be doubted whether it was prudent considering the circumstances of the case. In the first place, it meant the loss of enormous territories for some of the Protestant princes who had enriched themselves from the lands of the bishops and abbots. During the earlier stages of the war many of those men had stood loyally by the Emperor in his struggle against rebels and foreign invaders, but now, mindful of their own temporal interests and the future of their religion, they were prepared to range themselves on the side of their co-religionists in what had become purely a religious war. France, too, alarmed by the victory of Ferdinand II., and fearing that a victory for the House of Habsburg might lead to the establishment of a united empire and the indefinite postponement of the project of securing for France the provinces along the Rhine, was only too glad to pledge its support to the Protestant princes in the war against the Emperor. The young and valiant king of Sweden, Gustavus Adolphus, was a keen spectator of the trend of affairs in Germany, and was anxious to secure for his country the German provinces along the shores of the Baltic. He was not without hopes also that, by putting himself forward as the champion of Protestantism and by helping the Protestant princes to overthrow the House of Habsburg, he might set up for himself on the ruins of the Holy Roman Empire a great Protestant confederacy embracing most of Northern Europe. Finally, even though Saxony had been induced by special concessions to accept the Edict of Restitution, it might have been anticipated that in a purely religious struggle between Catholics and Protestants hatred of the Roman Church would prove stronger than the prejudices against Geneva, and its ruler would be forced to join the enemies of the Emperor.

Gustavus Adolphus, having strengthened himself by a formal agreement with France, marched into Germany at the head of a body of picked troops (1630). He issued a proclamation announcing that he had come to free the Germans from slavery, and he opened negotiations with the Protestant princes, some of whom to do them justice showed themselves very reluctant to become allies of a foreign invader. Ferdinand II. was but poorly prepared to meet such an attack. The imperial troops had been disbanded, and what was much worse, Wallenstein had retired into private life. Many of the Catholic princes, notably Maximilian of Bavaria, resented his rapid promotion and the grant that had been made to him of the Duchy of Mecklenburg. They prejudiced the mind of Ferdinand against him just at the time his services were most urgently required. Nor, when the first fit of zeal had passed away, were all the Catholic princes anxious to hasten to the support of the Emperor. Tilly with the forces of the /League/ advanced to bar the progress of the Swedes. He was defeated at Breitenfeld (1631) and his army was nearly destroyed. Gustavus Adolphus pushed rapidly forward towards Bavaria, captured the cities of Wurzburg, Mainz, and Augsburg, and for a time it seemed as if his advance to Vienna was going to be a triumphal march. Over-joyed with the success of his campaign he began to act as if he were really emperor of Germany, thereby giving great offence to many of his German followers. His dreams of power were, however, brought to an abrupt termination. In April 1632 he fought an indecisive battle at Rain on the Lech, where Tilly was wounded mortally, but in November he was slain at Lutzen though his army was victorious.

Ferdinand found himself in great danger. He appealed for aid to Urban VIII. and to Spain but at first the former, believing that the struggle was more political than religious, refused to assist him, though later on, when he realized that the very existence of the Catholic Church in the empire was endangered, he changed his mind and forwarded generous subsidies. Maximilian of Bavaria, who had held aloof for a time, espoused warmly the cause of the Emperor, and Wallenstein, who had been recalled in the hour of danger, raised an immense army in an incredibly short space of time. Oxenstierna, the chancellor of Sweden, took up the work of his master Adolphus and succeeded in bringing about an alliance with the Protestant princes (1633). So low had the national feeling sunk in the empire that the Protestant princes consented to appoint this upstart as director of the campaign and to fight under his command. France supplied the funds to enable the Swedes to carry on the war. For some time very little was done on either side. Negotiations were carried on by Wallenstein with the Swedes, with Saxony, and with France. It was represented to the Emperor that his chosen general was guilty of gross disloyalty. Though the charge of absolute disloyalty has not been proved, still certain actions of Wallenstein coupled with his inactivity gave good color to the accusation. The Emperor dismissed him from his command, and a little later he was murdered by some of his own soldiers.

The war and the negotiations were renewed alternately, but without any result as peace was not desired by either Sweden or France. At last the forces of the Emperor gained a signal victory at Nordlingen (1634). This success had at least one good result in that it detached the Elector of Saxony from the side of Sweden. He had never thrown himself whole-heartedly into the struggle, as he disliked the idea of supporting a foreign invader against his own Emperor, and was not sorry to escape from a very awkward position. The Peace of Prague was concluded between the Emperor and Saxony (1635), according to which the Edict of Restitution was abandoned in great measure, and religious freedom was guaranteed to the Protestants of Silesia.

But to promote their own interests the Swedes and the French insisted on complete equality between the Protestants and Catholics as an indispensable condition for peace. From this time onward it was a purely political struggle, inspired solely by the desire of these two countries to weaken Germany and to break the power of the House of Habsburg. On the death of Ferdinand II. in 1637 it was thought that the war might have been ended, but these hopes were disappointed. Ferdinand III. (1637-57) who succeeded offered a general amnesty at the Diet of Regensburg (1641) without avail. French soldiers crossed the frontiers to support the Swedes and the Protestants. Finally after long negotiations the Peace of Westphalia (1648) put an end to a struggle, in which Germany had suffered enormously, and from which foreigners were to derive the greatest benefits.

The Peace of Westphalia was dictated to Germany by France and Sweden. As a reward for the injury they had inflicted on the country both received large slices of German territory. France insisted on getting possession of Alsace, while Sweden received large grants of territory along the Baltic together with a war indemnity of five million thalers. In order to provide compensation for the secular princes, portion of whose territories had been ceded to these two powers, and also to reward others who had suffered for their alliance with Sweden, the secularization of a considerable amount of the ecclesiastical states was arranged. Saxony, Brandenburg, Hesse-Cassel, Brunswick, and Mecklenburg were enriched by the acquisition of lands formerly ruled over by the bishops and abbots. This step meant that the Protestant states of Germany were strengthened at the expense of the Catholic Church, and that the people of these districts being now transferred to Protestant rulers were in great danger of being drawn over to the religion of their new masters. The jurisdiction of the bishops was abolished in these territories, and even in some of the new chapters, as for example at Osnabruck, Protestant canons were installed side by side with Catholics.

Furthermore, it was arranged that the terms of the Peace of Augsburg should be observed, with this important change, that the rights guaranteed in it to the Lutherans should be extended even to those who did not accept the Augsburg Confession. This concession was intended to meet the demands of the Calvinists. Again, complete equality was established between Catholics and Protestants in the empire. To give effect to this clause it was arranged that in all imperial committees and courts both parties should be represented in equal numbers. In case religious issues were discussed at the Diet, where the Catholics still had the majority, it was agreed that the matter should not be decided by voting but by friendly compromise. The princes were permitted to determine the religion of their subjects, the principal restriction being that those subjects who were in the enjoyment of a certain form of public or private religious worship in 1624 should not be forced to change their religion. For the others nothing remained but to seek a home where their conscientious convictions might be respected. In regard to ecclesiastical property the year 1624 was taken as the normal year, the property that the Protestants held in that year being allowed to remain in their hands. The Ecclesiasticum Reservatum clause was retained, and made obligatory on both parties. These terms, it was provided, should not extend to the Protestants in the hereditary dominions of the Emperor.

The Peace of Westphalia by its practical recognition of state neutrality in religious matters put an end to the constitution of the Holy Roman Empire, and reduced the Emperor to the position of a mere figurehead, depending for strength entirely on his own hereditary states. Instead of preventing disunion it made national unity almost impossible, and exposed Germany to attack from any hostile neighbor who might wish to strengthen himself by encouraging strife amongst its various states. Besides, it inflicted a severe injury on the Church not merely by its recognition of the Protestant religion, but by the seizure of ecclesiastical property, the abolition of bishoprics, the interference with cathedral chapters, and the recognition of the right of the temporal sovereign to determine the religion of his subjects. It was no wonder then that the papal legate Fabio Chigi lodged a strong protest against the Peace, and that the protest was renewed in the most solemn form by Innocent X. (1648). This action was not inspired by the Pope's opposition to peace. On the contrary, again and again during the civil war the Holy See had sought to bring about a friendly understanding, but no Pope, unless he was disloyal to the trust confided in him, could permit such interference in purely religious matters without making it clear that he was not a consenting party. Innocent X. foresaw that this was but the herald of new claims on the part of the civil rulers, and that in a short time even the Catholic sovereigns would endeavor to regulate the ecclesiastical affairs of their subjects without reference to the authority of the Church. Nor was it long until events showed that his suspicions were not without good foundation.