The Thirty Years' War began as a conflict between Catholic and Protestant forces in Central Europe and the Holy Roman Empire, but as the war wore on it evolved into a continuation of the centuries long battle for continental supremacy between the Bourbons of France and the Hapsburgs of the Holy Roman Empire. The Thirty Years' War is often broken down into four distinct phases—The Bohemian Phase, the Danish Phase, the Swedish Phase, and the French Phase.

Gustavus Adolphus was the commander of the Swedish forces throughout the Thirty Years' War. Victory of his army at the Battle of Brietenfield prevented the Hapsburg forces from reunifying the German-speaking world under the Catholic faith.

Gustavus Adolphus was the commander of the Swedish forces during the Thirty Years' War. Sweden fought on the side of Protestantism and the anti-Hapsburg side.

Erasmus is one of the most celebrated men of the Northern Renaissance. He was born in the Netherlands and lived his whole life as a staunch Catholic. He was however greatly disturbed by the abuses of the clergy within the Catholic Church. He worked tirelessly to try and reform the Church from within. He had many supporters within the humanist and renaissance movement, but was widely condemned by the more polemical supporters from both the Catholic and Protestant camps.

The Protestant Reformation began in 1517 when Martin Luther wrote his 95 Theses on the abuses and malpractice of the Catholic Church and nailed them to the door of a church in Wittenberg.

The Diet of Worms convened in 1521, just four years after Luther posted his 95 Theses and somewhat inadvertently began the Protestant Reformation. The Diet was convened by Charles V and the Holy Roman Empire in order to discuss Luther's challenges to the church and what should be done about him. Luther was called to speak before the Diet, and when he did so was condemned as a heretic. The Diet of Worms resulted in the Edict of Worms, which declared Luther a heretic and all those who followed his teachings as giving up the right to life. Many Princes ignored this ruling, as did many common people, and Luther's influence continued to grow in spite of the church's best efforts.

All of these people were responsible for spreading or encouraging the break from the Catholic Church that occurred during the Protestant Reformation. Luther sparked the Reformation with his 95 Theses; Calvin and Zwingli adapted and spread the ideas in France and Switzerland; and Henry VIII founded the Church of England and placed himself as head of Christianity in England.

The Peace of Augsburg allowed the ruling Princes of the Holy Roman Empire to determine for their kingdoms whether they would be ruled as a Lutheran or Catholic state; however, the two other major Protestant religions of continental Europe—Calvinism and Anabaptism—were excluded. This would have significant consequences for the next hundred years of European history. Anabaptists were routinely massacred (as in the famous Siege of Munster) and Calvinists were persecuted to the point where, in their desperation, they provided one of the main catalysts for the devastating Thirty Years' War.

The Presbyterian Church is a branch of Calvinism that arose in Scotland during the sixteenth century. It was widely influenced by the Scottish theologian and protestant reformer, John Knox, who lived and studied with Calvin in Geneva and then returned to Scotland, bringing the new faith with him.

The Munster Rebellion took place from 1534 to 1535 in Munster, Germany. The rebellion began when Anabaptist community leaders took control of the city and instituted an egalitarian religious government. Anabaptists believed that all people were equal before God and that all things, including wealth and income, should be shared equally. This, along with many of the other religious beliefs of the Anabaptists, was considered extremely dangerous to the established order, and the rebellion was put down brutally.