The Great Schism of 1378 involved a split in the Roman Catholic Church. For several years in the fourteenth and early-fifteenth centuries, there were effectively two popes claiming legitimate authority over the whole of Christianity: one in France and one in Rome.

Martin Luther, a German priest and theologian, wrote the 95 Theses in protest against many of the teachings of the Roman Catholic Church.

The belief that God does not exist is called “atheism;” the belief that God may or may not exist, but “I need to see proof for myself” is called “agnosticism.” Deism is the belief that God created the universe with certain permanent laws (the law of gravity and so on) and then sat back and left creation to its own devices: essentially a “watchmaker God,” who created the world and then left it alone. Deism grew in popularity during the so-called Age of Reason in Europe, when scientists and thinkers like Newton began to uncover certain seemingly perfect laws about the universe.

The Crusades were a series of religious wars fought between Christian forces of Europe and Muslim armies of the Middle East. Most of the conflict took place over Middle Eastern territory considered sacred by both faiths. The other answers are incorrect because they refer to other historically opposing forces, several of which did not fight wars with each other.

John Calvin (1509-1564) was an influential theologian whose teachings formed the basis a wide array of newly formed churches. Chief among Calvin's theological differences from the Catholic church was his belief in predestined salvation. According to Calvin, God was absolutely sovereign in all matters of salvation, meaning that works and faith by human beings are worthless, no matter how good, without being chosen by God for salvation. Rather unintuitively, this led Calvin to preach that moral rectitude in every facet of life was of the utmost importance. Surely, if one had been chosen for salvation by God, he argued, then one had to be of the highest character and ought to show it.

Martin Luther wrote the 95 Theses, in which he questioned and criticized many practices of the Catholic church, including indulgences (reduction of punishment for a sin), which many church members were abusing by commercializing the process. These questions would spark change resulting in the Protestant Reformation.

Thomas Aquinas was a renowned Catholic philosopher and lived before the Reformation, so he would not be the best answer. Martin Luther King, Jr. lived far after the Protestant Reformation, so he would not be a good answer here. Henry VIII lived during the Protestant Reformation and became the head of the church of England, but he did not publish the work in question, so he would not be the best choice. Finally, Martin Luther was an important figure in the Reformation and he published the work in question, so he would be the correct answer.

The prestige of the Papacy declined significantly in the decades leading up to the Protestant Reformation. The Babylonian Captivity of the Papacy, a fourteenth-century event in which popes were held in Avignon by the French King, and the Great Schism, in which two separate popes, one in Rome and one in France, were elected for several decades, both contributed negatively to the prestige of the Papacy. The Pope’s involvement in secular politics also contributed to the declining prestige of the Papacy, as it angered the rulers of Europe and inspired disdain from intellectuals. Finally, the rise of humanism put a greater emphasis on the abilities and virtues of man and less emphasis on salvation. The Italian city states were only gaining wealth in this time period, so this answer choice cannot be said to have contributed to the declining prestige of the Papacy.

Jan Hus and John Wycliffe were both European religious reformers in the centuries leading up to the Protestant Reformation. Both men emphasized personal communion with God and diminished the significance of the Church as the only path to salvation.

Indulgences were sold throughout the medieval period in Europe by the Catholic church as a means to grant oneself forgiveness for sins or to gain forgiveness for someone who had died. The idea was the Catholic church was in charge of dispensing “merit” so that people could enter into heaven and that those who give financially to the church should benefit. They became extremely popular in 1517, when Pope Leo X sold indulgences to build a new St. Peter’s Basilica, as many people attempted to gain forgiveness. The selling of indulgences outraged Martin Luther, who mentioned them throughout his 95 Theses and fought against them as one of his main issues for reform. In 1567, the church outlawed the selling of indulgences.