How should nations organize themselves to maximize their security in the modern world? Whereas inter-state relationships have prevailed in the world to date, non-state and intra-state security threats have become more salient in the 21^st century. Clearly, significant co-operation among states is necessary to successfully confront specific non-state security threats like terrorism and transnational organized crime. But the form and nature of this co-operation vary widely and depend on many political and contextual issues that can sometimes constrain a state’s effectiveness in confronting such non-state threats.