There were a lot of countries, but they were not equally powerful or important. Although the Big Ones had agreed not to eat the Little Ones, the Little Ones still walked softly around the Big Ones. The Great Powers were Britain, France, Germany, the Austro-Hungarian Empire, and Russia. Italy was a “Great Power” only by way of courtesy.[1]

The Minor Powers were the Scandinavian countries (Norway, Denmark, Sweden); the Low Countries (Belgium, Holland); the Iberian countries (Spain, Portugal); and the Balkan countries (Serbia, Rumania, Bulgaria, Greece).

Beyond Europe there were countries that were rising up into (the United States, Japan) or falling down out of (the Ottoman Empire) the ranks of the powers.

The core idea of 19^th Century diplomacy was to maintain the five Great Powers in relative equilibrium so that no one state could dominate all the others. If one state or two allied states threatened to become too powerful, then the other states would align against it.

There were four key elements in maintaining this Balance of Power.

1. “Compensation.” That is, the point of the balance of power was to keep everyone at approximately equal strength. If one Great Power increased its strength by adding territory, then the other Great Powers had to be “compensated” in order to increase their strength. Lots of times this compensation was purely symbolic, rather than substantial. Great Powers just didn’t want to be seen by other countries as not being important. Then, who paid the “compensation”? Little countries or faraway places, that’s who. That was one of the down-sides to being a Lesser Power or not a power at all. People took stuff away from you and you just had to lump it.
2. Constant maneuvering. Most treaties were not permanent or open-ended. They had time limitations because states made arrangements to deal with specific problems that came up. Both countries had to agree to renew a treaty when it expired or to end it ahead of time. If one or both parties chose to not re-new a treaty, then it ended. In theory, both walked away with no hard feelings.
3. Self-restraint. Just because you can do something right now, doesn’t mean that you should do it. A selfish pursuit of individual national interest will destabilize the system. Other countries will start thinking of your country as a problem. They’ll start thinking about how to re-direct you. If you get three or four other Great Powers thinking about how to re-direct you, then you will get re-directed. Look at Germany in the 20^th Century.
4. The absence of ideology as a factor in decision. Liberalism and Conservatism are ideologies. Communism and Fascism are ideologies. In Balance of Power politics, these don’t matter in deciding on international alignments. OK, probably you think Democratic countries are natural allies against Dictatorships. That isn’t true in Balance of Power politics. After 1870, Britain and France had the most democratic governments in Europe, but they were constantly at odds over colonial disputes. In 1894 Republican, democratic France formed an alliance with autocratic Tsarist Russia. Both had a need for an ally, so they made nice with each other in spite of the vast differences in their domestic politics. Countries didn’t have “permanent friends.” They had permanent “interests.”

[1] Usually, no one cared what the Italians thought. They just pretended that they did. This is called “having good manners.”