Formation of a broad alliance of most major actors in an international system for the purpose of jointly opposing aggression by any actor. Kant: majority of states can come together to punish one state. League of nations was formed to promote collective security. Membership did not include all great powers. Members proved unwilling to bear to costs of collective action to oppose aggression when it occurred. Depends on members keeping commitments and enough members have to agree on what constitutes aggression. Worked in iraq"s conquest of kuwait because aggression brought all the great powers together and because they were willing to bear costs on confronting iraq. Collective security: coalition building strategy in which a group of nations agree not to attack each other and to defend each other against an attack from one of the others. All for one and one for all. Us operation enduring freedom (october 7 2001) Official goal: find osama bin laden; destroy haven for terrorist.