This is an excellent question because it addresses what is perhaps the key problem of the United Nations.
What follows are my thoughts on collective security and a non-specific discussion on the Leage and the UN's own failings in this area. It is not intended to be an essay response to the question so much as a potential guide for your own research or aide to your own thought process.
The concept of collective security is that a group of countries united together would be able to better provide for the common defense if any single member were attacked. Indeed, the very fact that numerous countries are obligated to respond to any attack, would serve to deter would-be aggressors.
Well, before we take a look at the United Nations and its predecessor, let's examine an even better example of the principle of collective security at work - the NATO alliance.
NATO is perhaps the most successful and longest-lasting "collective security" alliance in history. NATO helped to cement the democratic countries of Western Europe together during the Cold War and served to counter and deter the Soviet Union and Warsaw Pact alliances.
But the reality is that NATO was always totally dependent on the United States. The British, the W. Germans, and the French (sort of) all contributed major forces, but when push came to shove it was America that was providing the backbone in terms of troops and money. In fact, NATO was in large part founded with the European aim to keep America engaged on the European continent.
Throughout the Cold War, NATO "kept the peace." The reailty, however, is that many of the NATO countries did little to contribute. ...
The solution tackles collective international security based on the nature of the international relations system.