The current complexities of national security in the post-9/11 context have become far more complex than the view of some who believed that the end of the bipolar Cold War struggle would ease tensions between states. While the United States experienced a reduction in historic threats from the Soviet Union, other states continued to experience internal and external security challenges. Theresa Reinold's article, published in 2011 in the American Journal of International Law, examines the need to modernize and clarify the criteria that will govern the defensive use of force by states against other states that are unable or unwilling regulate the actions of irregular forces located within the territory of their state. Reinold accepts that the 21st century introduced the global community to mass terrorism during 9/11, requiring states to protect their own security, while rationalizing that uncontrolled use of force in the name of self-defense would also set a dangerous precedent . Key elements of Reinold's analysis are the inability and unwillingness to exercise control over irregular forces within the haven state. States are also changing their interpretation of international norms of self-defense which have historically included the principles of immediacy of attack, the requirement of attribution to the State, and the duel requirement of necessity and proportionality. The author's objective analysis of this critical topic provides an intriguing and thoughtful study using recent conflicts in Lebanon, Colombia, and Pakistan. One might refer to Grotius's 1625 writing which foresaw these challenges: “That the possibility of being attacked confers the right to attack is abominable for any prince...... middle of paper ......tes has brought to a broader interpretation of what qualifies as a fair use of force under the jus ad bellum. The world community changed forever after the September 11 attacks, and this event ushered in a reinterpretation of when a state can act after another state's unwillingness or inability to provide security. Reinold presented plenty of evidence that norms have changed. World opinion has relatively accepted this shift to the use of force, but at the same time every situation is complex and different. The cases presented present aspects that support both positions leading to thorny debates and this could be true for many other crises around the world. This article presents a relevant topic that will continue to evolve and lead to careful scrutiny as globalization increases and states require other states to accept changing security norms.