This is taken from History of the Catholic Church.

For more than thirty years the new religious movement continued to spread with alarming rapidity. Nation after nation either fell away from the center of unity or wavered as to the attitude that should be adopted towards the conflicting claims of Rome, Wittenberg, and Geneva, till at last it seemed not unlikely that Catholicism was to be confined within the territorial boundaries of Italy, Spain, and Portugal. That the world was well prepared for such an upheaval has been shown already, but it is necessary to emphasize the fact that the real interests of religion played but a secondary part in the success of the Protestant revolt. Luther, Calvin, Zwingli, and Knox may be taken as typical of the new apostles, and however gifted and energetic these men may have been, yet few would care to contend that either in their own lives or in the means to which they had recourse for propagating their views they can be regarded as ideal religious reformers.

Protestantism owed its success largely to political causes, and particularly in the case of Lutheranism to its acknowledgment of the principle of royal supremacy. At its inception it was favored by the almost universal jealousy of the House of Habsburg and by the danger of a Turkish invasion. If attention be directed to the countries where it attained its largest measure of success, it will be found that in Germany this success was due mainly to the distrust of the Emperor entertained by the princes and their desire to strengthen their own authority against both the Emperor and the people; in Switzerland to the political aspirations of the populous and manufacturing cantons and their eagerness to resist the encroachments of the House of Savoy; in the Scandinavian North to the efforts of ambitious rulers anxious to free themselves from the restrictions imposed upon their authority by the nobles and bishops; in the Netherlands to the determination of the people to maintain their old laws and constitutions in face of the domineering policy of Philip II.; in France to the attitude of the rulers who disliked the Catholic Church as being the enemy of absolutism, and who were willing to maintain friendly relations with the German Protestants in the hope of weakening the Empire by civil war; in England, at first to the autocratic position of the sovereign, and later to a feeling of national patriotism that inspired Englishmen to resent the interference of foreigners in what they regarded as their domestic affairs; and in Scotland to the bitter rivalry of two factions one of which favored an alliance with France, the other, a union with England. In all these countries the hope of sharing in the plunder of the Church had a much greater influence in determining the attitude of both rulers and nobles than their zeal for reform, as the leaders of the so-called Reformation had soon good reason to recognize and to deplore.

Protestantism had reached the zenith of its power on the Continent in 1555. At that time everything seemed to indicate its permanent success, but soon under the Providence of God the tide began to turn, and instead of being able to make further conquests it found it impossible to retain those that had been made. The few traces of heresy that might have been detected in Italy, Spain, and Portugal disappeared. France, thanks largely to the energy of the League and the political schemes of Cardinal Richelieu, put an end to the Calvinist domination. Hungary and Poland were wrested to a great extent from the influence of the Protestant preachers by the labors of the Jesuits. Belgium was retained for Spain and for Catholicity more by the prudence and diplomacy of Farnese than by the violence of Alva; and in the German Empire the courageous stand made by some of the princes, notably Maximilian of Bavaria, delivered Austria, Bohemia, Bavaria and the greater part of Southern Germany from Protestantism.

Many causes helped to bring about this striking reaction towards Catholicism. Amongst the principal of these were the reforms initiated by the Council of Trent, the rise of zealous ecclesiastics and above all of zealous popes, the establishment of new religious orders, especially the establishment of the Society of Jesus, and finally the determination of some of the Catholic princes to meet force by force. Mention should be made too of the wonderful outburst of missionary zeal that helped to win over new races and new peoples in the East and the West at a time when so many of the favored nations of Europe had renounced or were threatening to renounce their allegiance to the Church of Rome.