Gustavus Adolphus was killed in battle in 1632, ending Sweden's active leadership in the Protestant cause. In the last phase of theThirty Years’ War, the most dominant player on the Protestant side was Catholic France. Granted, the French had a bit of help from the Swedes, who had switched roles from fighter to financier.
The last phase of the Thirty Years’ War was the bloodiest and failed to produce a decisive result. After thirty years, people were weary of war and had lost track of why they were even fighting. The warring parties gathered at Westphalia to hammer out a rational peace to end a long war that had begun as a local religious conflict.