The balance of power is the idea that the national security of a nation is expanded through military conquest and it's distributed so that one state won't be able to dominate all others. That if one nation gains that power to dominate other nations, it will use that power to attack weaker nations and continue to expand. The balance of power of European states changed from 1848 to 1914 because of revolutions and certain unifications. Like the nationalistic unification of Italy and Germany. And certain imperialistic changes that led to unifications. Also certain the Crimean War, which caused the end of conservatism and alliances with European nations. From 1848-1914 there were many nationalistic, imperialistic, and certain failures that affected the balance of power among European states.
The unification of Italy started with a man named Count Camillo Benso di Cavour. He was a nobleman who had limited and realistic nationalistic goals when he joined politics of Sardinia. He wanted unity for northern and central Italy for a more expanded kingdom of Sardinia. Cavour worked to make Sardinia a liberal constitutional state capable of leading Italy, though he wanted to build highways and expand civil liberties, he couldn't expand without a powerful ally. Austria was in the north and Sardinia was small and weak against Austria, so Cavour formed a secret alliance with Napoleon III in July of 1858. Cavour goaded Austria into attacking Sardinia and got the help from Napoleon to push Austria out of the north, expanding Sardinia. But Napoleon was worried for criticism for supporting the pope's declared enemy, so he made a peace with Austria and granted only Lombardi and the area around Milan to Sardinia. Cavour eventually resigned out of rage. Later Cavour's allies followed through with unifying Italy, but pro-Sardinian nationalists encouraged revolts. The middle-class nationalistic leaders in central Italy wanted a fusion with Sardinia.