Today's national security complexities in the post-9/11 environment have become far more complex than was believed by some who believed that the end of the bipolar struggle of the Cold War would appease the tensions between states. While the United States has experienced a reduction in historic threats from the Soviet Union, other states have continued to face 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 cannot or do not want to regulate the actions of irregular forces located on the territory of their state. Reinold admits that the 21st century introduced the global community to mass terrorism during 9/11, requiring states to protect their security, while explaining that the uncontrolled use of force in the name of self-defense would also create a dangerous precedent. The key elements of Reinold's analysis are the inability and refusal to exercise control over irregular forces within the host state. States are also changing their interpretation of international norms of self-defense, which historically include the principles of immediacy of attack, the requirement of attribution to the state, and the requirement of necessity and proportionality. The author's objective analysis of this critical topic makes for an intriguing and thoughtful study using recent conflicts in Lebanon, Colombia, and Pakistan. We could refer to the writings of Grotius from 1625 who foresaw these challenges: "The fact that the possibility of being attacked confers the right to attack is odious to any prince...... middle of paper.. . led to a broader interpretation of what constitutes a just use of force under jus ad bellum. The global community changed forever after the September 11 attacks, and this event marked the beginning of a reinterpretation of when a state can act after another state's refusal or inability to provide security. Reinold presented ample evidence that standards have changed. World opinion has become relatively tolerant of this shift to the use of force, but at the same time, each situation is complex and different. The cases presented present aspects that support both positions, giving rise 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 attract much scrutiny as globalization increases and states demand that other states accept changing security standards..