Key justifications include responding to direct aggression, preventing imminent threats, honoring collective defense commitments (e.g., NATO), and, in specific cases, intervening for humanitarian reasons. Self-Defense and Security: The primary justification is responding to a direct attack on U.S. territory, troops, or citizens. The President is authorized to repel such attacks. Defense of Allies and Collective Security: Engaging in war to protect allies and fulfill alliance obligations, such as Article 5 of the North Atlantic Treaty. Protection of International Order: Intervening to stop flagrant violations of international law, aggression, or to restore regional stability. Humanitarian Intervention: Preventing mass atrocities or genocide, especially when they threaten international peace or basic human rights. Preemptive Action: Acting against an imminent, or sometimes perceived as imminent, threat to national security. Countering Proliferation and Terrorism: Protecting against the spread of weapons of mass destruction or organizations deemed hostile to the U.S. and its allies. the president can only introduce U.S. armed forces into hostilities or where hostilities are imminent if Congress has passed a declaration of war or specific statutory authorization (such as an AUMF) or where there is a “national emergency created by attack upon the United States, its territories or possessions, or its armed forces.” The WPR also requires any hostilities, conducted without a declaration of war or specific statutory authorization, to be terminated within 60 days, and provides a mechanism for Congress to order the termination of any such hostilities. While the WPR has often been misconstrued as an instrument that provides affirmative authority to the president to use force, this is not the case. Rather, the WPR provides a framework for the existing constitutional division of war powers between Congress and the executive branch, discussed above.Any use of force that is not within these parameters and has not been authorized by Congress would be unconstitutional. Beloud