Before 1517, there was only one acceptable religion in Europe----Roman Catholicism. No choice, no voice, no way out. This is what several people thought about their religious rights. If you were not a Catholic, you were not going to last very long. Europe needed to be religiously reformed. Hence, the Protestant (and Counter) Reformation.
The Reformation bloomed with a man named Martin Lither. Formerly a monk, and a devout religious man, Luther had strong opinions about the ways things worked in the church. He criticized the corrupt clergy and misplaced self righteousness of the Pope. With that, he had started a revolt still goes on today. Martin Luther and his followers, Lutherans, formed their own religion. Others followed, including leaders such as John Calvin, Ignatius, and Zwingli. Soon there were all types of religions all over Europe. All had to fight to earn their right to practice as they desired. This caused national turmoil, countless wars, and separation.