Final answer:
The major impact of the Protestant Reformation in the German states was the devastation of the Thirty Years' War. Therefore, the correct option is D devastation of the Thirty Years' War.
Step-by-step explanation:
The major impact of the Protestant Reformation in the German states was the devastation of the Thirty Years' War. This war, which lasted from 1618 to 1648, was fought between Catholic and Protestant states in the Holy Roman Empire. As the different religious factions fought each other, the German lands experienced widespread destruction as armies of mercenaries pillaged and destroyed farms and villages. In the end, the German Protestants emerged victorious, but the war had a lasting impact on the region.