The Protestant Reformation began in 1517 when Martin Luther nailed his 95 Theses to the door of a church in Wittenburg. It was not the first time in European history that a reformer had sought to make radical changes within Christianity to escape the abuses and power of the Catholic Church; however, it was the first time that such a reformation had been attempted since the invention of the printing press by Johannes Gutenberg in 1439. The printing press allowed Luther's work to be reprinted, translated and transmitted around Europe, spreading the ideas of the Protestant Reformation to a whole new host of people.

Following the reign of Henry VIII, English monarchs were expected to follow Anglicanism and be the head of the Church of England. Henry broke from the Catholic Church in 1535 and began the English Reformation. Mary, one of his daughters, reigned in between his son Edward and another of his daughters, Elizabeth I. She undid all the Reformation changes undertaken by her predecessors and declared England a Catholic kingdom. This would prove a costly mistake for her in terms of maintaining her power. For the rest of English history, English monarchs have rarely been Catholic and certainly have rarely been openly Catholic.

The Peace of Westphalia was a peace treaty signed in 1648 that ended the brutal Thirty Years' War that had ravaged much of Central Europe. The Thirty Years' War was primarily a conflict between Protestants and Catholics fought in the lands of modern-day Germany, but at one time or another it involved almost every major power in Europe.

The Peace of Augsburg was signed in 1555 between the Holy Roman Emperor Charles V and an alliance of Lutheran rulers within his empire. It declared that the various princes of the Holy Roman Empire were free to choose whichever denomination of Christianity they wanted for their dominion, but then the entire population of that territory had to follow the chosen religion.

Predestination is the belief that the fate of all people, and their access to the afterlife, is predetermined by God before they are born. This was a core tenet of Calvinism.

Huguenots were French Protestants during the Reformation in France and in some places still are today. They have been heavily persecuted throughout French history by various groups and often by the state, and their numbers have never been as high as they were before the French Wars of Religion. 

The Council of Trent convened in the middle of the sixteenth century. Its purpose was to provide an official Catholic response to the Protestant Reformation. In particular, the Council ruled on the various doctrines of faith that were being criticized by the Protestant Reformation and widely reaffirmed them. It also ruled that Bishops had to be present in the territory that they governed and that the sale of indulgences was an illegal church practice.

The Peace of Augsburg was signed in 1555 between Charles V, the head of the Holy Roman Empire, and an alliance of Lutheran Princes. The Peace formally ended hostilities between the two groups and permanently established the division of Christianity between Catholicism and Protestantism in the Holy Roman Empire. Although it provided some measure of "religious tolerance," to use that phrase suggests far more tolerance than was present at the time. Yes, the rulers of a princely state could determine which form of Christianity they wanted, but all their subjects had to obey on pain of death, and executions and genocides remained common throughout Europe.

The Defenestration of Prague occurred in 1618. It refers to an incident where a group of Catholic Lords were thrown out of a window following a rather heated disagreement with a group of Protestants. This incident is one of the most famous in the build-up to the Thirty Years' War, which would rage from 1618 until 1648 across much of Central Europe. 

In Anglicanism, the English monarch is head of the Church of England. In Anabaptism, adults are baptized rather than babies. Predestination, the belief that people's eternal fate is predetermined by God before they are born, is a core concept of Calvinism. Justification through Faith alone is the crucial difference between Lutheranism and Catholicism. Luther said that good works and following the rules of the Church were not the way through which eternal salvation was achieved. Instead, Luther argued that salvation was already promised, all one had to do was believe in it and have faith in Christ's saving grace.