This report explores how a nuclear-armed Iran would behave, if it would act aggressively, and what this would entail for the United States and its main regional allies, including the Gulf Cooperation Council (GCC) and Israel. The Islamic Republic seeks to undermine what it perceives to be the American-dominated order in the Middle East and to deter a U.S. and/or Israeli military attack, but it does not have territorial ambitions and does not seek to invade, conquer, or occupy other nations. Nuclear arms are unlikely to change its fundamental interests and strategies. Rather, they would probably reinforce Iran's traditional national security objectives. The ideological beliefs of the Iranian political elite will not shape the country's nuclear decisionmaking. The regional geopolitical environment and Iran's political, military, and economic capabilities will have a greater bearing on Iranian calculations. It is very unlikely that Iran would use nuclear weapons against another Muslim state or against Israel, given the latter's overwhelming conventional and nuclear military superiority. Further, the Iranian government does not use terrorism for ideological reasons. Instead, Iran's support for terrorism is motivated by cost and benefit calculations, with the aims of maintaining deterrence and preserving or expanding its influence in the Middle East. An inadvertent or accidental nuclear exchange between Israel and Iran is a dangerous possibility, but there is not much evidence to suggest that rogue elements could have easy access to Iranian nuclear weapons.

Introduction -- The Islamic Republic: a revisionist yet restrained power -- Possible motivations for nuclear weapons -- Nuclear weapons and internal instability -- Nuclear Iran and the Persian Gulf -- Revolutionary animosity and neighborly relations -- Limited ability to subvert the GCC -- Iran's military strategy and capabilities in the Persian Gulf -- Would a nuclear Iran close the Strait of Hormuz? -- Nuclear Iran and Israel -- An ideological, but not self-destructive, hatred of Israel -- Irrationality, command and control, and rogue actions -- Nuclear Iran and terrorism -- Iran's motives for supporting terrorism -- Extended nuclear deterrence -- Conclusion and findings.