Final answer:
The key tenet of nations joining together to guarantee each other's territory and independence against aggression is known as the collective security system. This principle forms the basis of international institutions such as the United Nations and is exemplified by alliances like NATO.
Step-by-step explanation:
The idea that all nations would join together to guarantee each other's territory and independence against aggression by any other nation is a key tenet of the collective security system.
This concept involves nations entering into agreements such as security pacts or alliances, where an attack against one member is considered an attack against all.
This idea is embodied in international institutions and agreements such as the League of Nations and later, the United Nations, although the specific term "collective security" is not explicitly mentioned in the United Nations Charter.
Rather, the idea is a foundation upon which the UN operates to maintain international peace and stability, as established after World War II.Collective security was a principle that President Wilson hoped would prevent future wars through the League of Nations, which he outlined in his Fourteen Points.
Although the United States did not join the League of Nations, the idea persisted and thrived with the establishment of the United Nations after World War II. Moreover, the concept of collective security is foundational to military alliances like NATO, which serve as modern examples of this principle in action.