One thing that is critical to understanding the Reformation is who it was that Luther convinced. He had no real interest in concern in the peasant toiling in the fields, or the craftsman or the merchant. The people who bought into Luther’s ideas were German princes, and that leads us back to crises between the Church and the Holy Roman Empire, that began with the Investiture Controversy four hundred years before. There had been growing restiveness for centuries between German rulers and Rome as Rome asserted an ever stronger role in temporal affairs, whilst the Holy Roman Emperors wanted to re-establish the Carolingian system with the Emperor in the pre-eminent position.
This cold war between Rome and German princes was further inflamed by the Avignon Papacy. For the German princes this represented a full co-opting of the Papacy by the French Kings. The Avignon Papacy pretty thoroughly discredited the institution in Northern Europe. The Church had gone from being the Emperor’s competitor, to being enslaved to the French Crown. While Charles V remained loyal to Rome, many other German princes saw Luther’s breach with Rome as the opportunity to make their own break, and here they had a ready-made theology. The common churchgoer in many parts of Germany and in Scandinavia were just along for the ride.
And Luther knew which side of the bread was buttered, because some of his most vociferous invective came as he gained royal backers. He had started at a position not a hundred miles away from Erasmus, and I’d argue that Luther didn’t say much, at least on theological grounds, that Augustine hadn’t said a thousand years before. But the key was that the Reformation was fundamentally political, the break from Rome wasn’t just over the nature of salvation or the sale of indulgences, it was part of a larger growing struggle between France and the Holy Roman Empire.