John Green teaches about the Protestant Reformation. Prior to the Protestant Reformation, pretty much everyone in Europe was a Roman Catholic. Not to get all great man, but Martin Luther changed all that. Martin Luther didn't like the corruption he saw in the church, especially the sale of indulgences, so he left the church and started his own. And it caught on! And it really did kind of change the world. The changes increased literacy and education, and some even say the Protestant Reformation was the beginning of Capitalism in Europe. [15:06]