be judged on a case-by-case basis. Collective defense Collective defense is an arrangement, usually formalized by a treaty and an organization, among participant states that commit support in defense of a member state if it is attacked by another state outside the organization. NATO is the best-known collective defense organization; its famous Article 5 calls on (but does not fully commit) member states to assist another member under attack. This article was invoked only after the September 11 attacks on the United States, after which other NATO members provided assistance to the US war on terror by participating in the War in Afghanistan. Collective defense has its roots in multiparty alliances and entails benefits as well as risks. On the one hand, by combining and pooling resources, it can reduce any single state's cost of providing fully for its security. For example, smaller members of NATO have leeway to invest a greater proportion of their budget on nonmilitary priorities, such as education or health, since they can count on other members to come to their defense if needed. On the other hand, collective defense also involves risky commitments. Member states can become embroiled in costly wars benefiting neither the direct victim nor the aggressor. In World War I, France was obligated to join into war with Austria-Hungary and Germany because France's ally Russia was at war with them. See also List of military alliances World War I World War II Franco-Russian Alliance Triple Alliance (1882) Anti-Comintern Pact Grand Alliance (World War II) Franco-Soviet Treaty of Mutual Assistance Germany–Soviet Union relations before 1941 Southeast Asia Treaty Organization Self-defence in international law References Works cited Bibliography Lowe, Vaughan, Adam Roberts, Jennifer Welsh and Dominik Zaum, The United Nations Security Council and War: The Evolution of Thought and Practice since 1945 Oxford: Oxford University Press, 2010, paperback, 794 pp. . Roberts, Adam and Dominik Zaum, Selective Security: War and the United Nations Security Council since 1945 (Adelphi Paper no. 395 of International Institute for Strategic Studies, London), Abingdon: Routledge, 2008, 93 pp. . External links de Wet, Erika, Wood, Michael. Collective Security, Max Planck Encyclopedia of Public International Law President Carter's Nobel Lecture International security Military alliances Germany–Soviet Union relations cs:Vojenský pakt