Which organization’s establishment primarily reflects the post-WWII application of collective security principles?

💡 Explanation:

The United Nations (UN) was established in 1945 following World War II with the core mandate of maintaining international peace and security through a system of collective security. This principle is defined by the idea that an attack on one member is considered an attack on all, an attempt to prevent future global conflicts. The League of Nations (A) was the failed pre-WWII attempt. NATO (B) is a regional collective defense alliance, not a global collective security organization. The European Union (D) is primarily an economic and political union.