This book examines the conditions that the United States must set to ensure that the international community will recognize the legitimacy of preemptive actions and avoid recrimination and isolation. Case studies will be examined within the framework initially laid out by the United States Secretary of State, Daniel Webster in the Caroline Case of 1842, imminence, necessity, and proportionality, and the impact the terrorist attack on 11 September. These evaluation criteria will be first used to evaluate three case studies drawn from the Israeli experience and political decisions in the 1967 Arab-Israeli War, the 1981 Israeli raid on the Iraqi nuclear facility at Osirak, and the 1982 invasion of Lebanon.The Israeli case studies establish an understanding of Webster's tenets of preemption, and the resulting isolation, from which threats identified by the United States National Security Strategy of 2002, can be evaluated. Under consideration are, respectively, a conventional threat, the development of weapons of mass destruction, and finally terrorism. The case studies used to illuminate these threats are the 2003 invasion of Iraq and potential conflicts with North Korea and Iran. Based on the legitimacy of the action, an attempt will be made to evaluate considerations required to establish conditions for a legitimate preemptive attack.