Looks like you forgot to add in the options but I will answer the best I can! The previous equilibrium was broken. During the 18th century the military strengths had been evenly divided between the two major alliances, but Napoleon had tipped the scales. With a powerful army, he had managed to crush all his opponents except Britain and Russia, creating a continental empire. Defeating him had required a massive joint effort from the other powers. The turning point was the battle of Leipzig in October 1813, in which more than half a million soldiers took part.
Worse still, the Napoleonic wars had shattered borders and broken political institutions in several parts of the Continent, especially in Germany. In order to heal its wounds, Europe needed peace. Hence the first priority was to preserve it from two of its chronic problems: hegemonic adventures (so there would never again be a Napoleonic empire) and internecine wars (so there would be no reasons to fight each other).
