Which organization, alongside NATO, does the US participate in for collective security?

The United Nations (UN) is a significant organization where the United States participates in collective security efforts alongside NATO. The UN plays a crucial role in promoting international peace and security through various means, including peacekeeping missions, conflict resolution, and the establishment of international norms and laws designed to regulate states' conduct towards one another.

The UN Security Council, which includes the United States as a permanent member with veto power, is primarily responsible for addressing threats to peace and can authorize collective action, including military interventions, if necessary. This framework allows countries to collaborate on security issues and respond collectively to crises, making it a vital component of global security architecture.

In contrast, the other organizations mentioned do not primarily focus on collective security in the same way. The European Union, while it does include security elements, primarily focuses on political and economic integration among its member states. The Association of Southeast Asian Nations promotes regional cooperation but is largely focused on economic and cultural issues rather than direct military alliances. The African Union also emphasizes political and economic cohesion within Africa, but its collective security measures are less centralized compared to the arrangements found in NATO and the UN.