Which nation emerged stronger after the Thirty Years' War?
I do not think that the 30 Years War was really good for any nation, but I suppose that you could at least make the argument that France emerged stronger after this war. The Holy Roman Empire was the clear loser.
The major reason that France emerged stronger from this war was because Spain was hurt so badly by the war. The Spanish Habsburgs were hurt by the extent to which the Holy Roman Empire (also in Habsburg hands) was a loser in the war. This led to the French being able to dominate the Spanish in the years after the end of the 30 Years War.