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.

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.

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.

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 reformation was a 16^th century cultural and religious upheaval that challenged the views of the Catholic Church and the Pope. At the time, the Catholic Church had enormous political and religious power. The reformers were angry about the corrupt practices of the church, such as selling indulgences (something that one pays for that reduces the amount of punishment one will have to undergo their sins) and believed that the bible, rather than the leaders of the Catholic church should be the ultimate authority. In 1517 Martin Luther nailed a list of “95 Theses” (complaints) on the door to Wittenberg Catholic Church, a document that would later become the basis of the Protestant reformation. Tensions continued to rise and bloody conflicts broke out all over Europe over different Christian sects and how to best worship god. These small wars culminated in the bloody 30 years’ war which killed somewhere between 25-40% of Germany’s population. The peace of Westphalia allowed freedom of religion for Christians, ended several land and independence disputes, and broke the political power of the Catholic Church. Many experts say that the Peace of Westphalia began the modern method of diplomacy.

John Calvin was a prominent French theologian and pastor during the fourteenth century. He preached predestination and the absolute sovereignty of God in determining the fate of souls. His beliefs were a major influence on the branch of Protestantism commonly referred to as Calvinism.