One of the most significant events post-Reformation for the history of theology was the teaching of Jacob Arminius. Arminius considered himself to be a true Calvinist, in the sense of being faithful to the teachings of John Calvin. However, Arminius developed a theology the reinterpreted the idea of predestination. Predestination was more about God having foreknowledge of who would believe than God determining who would believe.
Today, many protestant Christians divide themselves into those who identify as Calvinist and those who identify as Arminian. This video will help to understand how that divide emerged.