Martin Luther was able to form a new religion in no small part because he appealed to the desire of German princes for independence from Rome. At one point he wrote "Some have estimated that every year more than 300,000 gulden find their way from Germany to Italy … We here come to the heart of the matter. … How comes it that we Germans must put up with such robbery and such extortion of our property at the hands of the pope?"
The Protestant movement coincided with the emergence of nation-states as the new dominant institution in the West. Having a state religion made it easier for the head of state to maintain control. It also became a catalyst for centuries of wars that were fought by parties who saw little difference between religious affliation and patriotism.
In this is the still unfortunate residue of the Protestant innovation in religion. At its best, the Protestant faith shows an independence from church dogma that characterized centuries of the Roman Catholic monopoly on thought. At its worst, it becomes an adjunct to the feelings of national superiority that justify violence or injustice.
At its best, religion transcends national boundaries. At its worst, it becomes apologist for the meanest of nationalist feelings.