Nothing. Catholics are the first Christians. In fact, prior to 1517, all Christians were Catholic (and Orthodox). However, Martin Luther, a Catholic priest from Germany, broke away from the Church after expressing frustration with the Pope regarding some issues that he saw as leading to corruption and abuse. At that time, Germany, never fond of the amount of influence Rome had over politics in the developing world, was happy to get behind Luther and support his break from Rome. Thus, the Lutheran church was established. Since then, others who disagreed with Luther, and/or empowered by their own independent desires, established their own brands of Christianity. Sadly, D.I.Y. Christianity has resulted in tens of thousands of Christian denominations and independent churches all claiming to be strictly based on the Bible, while disagreeing with one another on almost every matter of faith.