Which organization provides collective security and defense through a treaty among member states?

• A. World Bank
• B. United Nations
• C. European Union
• D. NATO

Answer: (D)

Collective security through a formal treaty among member states is the defining feature here. NATO embodies this idea as a military alliance created after World War II through the North Atlantic Treaty, where member countries commit to mutual defense. The core requirement is that an armed attack on one member is considered an attack on all, prompting a united response. That treaty-based obligation makes NATO a dedicated defense framework among nations. In contrast, the World Bank focuses on financing development, the United Nations works on international peace and security more broadly without a standing mutual-defense obligation, and the European Union has security aims but does not function as a universal mutual defense pact like NATO. Therefore, NATO is the organization that provides collective security and defense through a treaty among member states.