Johann Tetzel sold indulgences in exchange for money, instead of good deeds. This was a major sign of Church corruption.
Come get your indulgences! Indulgences right here!
A professor and monk by the name of Martin Luther was not happy about this and wanted to stop Church corruption like this.
What is going on here!?
Martin Luther then wrote the 95 Theses, which are basically disagreements with the Church's decisions that lead it to corruption.
Selling indulgences isn't cool.
The Holy Roman Emperor Charles V, told Martin Luther to recant, which means to give up your views. Luther refused so Charles V made him an outlaw.
Even with Luther in hiding, people such as German people, German princes, and some clergy members, started to believe in Lutheranism.
I'm Lutheran now!
After all of the Protestant Reformation, I believe that even more people will start to put out their ideas on how to make the Church better. The effect that will have is people having fiery, religious wars over what they think is best for the Church.