Iraq south of Baghdad – that is, the country’s Shiite-dominated area – would also be left unchallenged for the time being. ISIS is a Sunni entity and aspires to destroy Shiism worldwide, but, like the Peshmerga, Iraq’s Shiite militias are battle-ready, and they hate Islamic State viscerally. Moreover, there is the Iran factor. Tehran is backing Iraqi Shiites – providing weapons and personnel – and ISIS will not want to challenge Iran, so will avoid attacking Iraqi Shiite territory. Whether to target Baghdad itself will be a strategic decision for ISIS. (Council on Foreign Relations President Richard Haass considers Baghdad already part of a Greater Iran.) Turkey, for its part, has already accepted Islamic State control over substantial territory along the Turkish-Syrian border. Ankara did not engage ISIS when the group attacked the Syrian Kurdish border town of Kobani, and Ankara has little reason to fight to save Syrian territory now, especially since it wants the Assad regime demolished. A victorious ISIS furthermore would have defeated and/or incorporated the various anti-Assad rebel groups, including the so-called moderates as well as al Qaeda-linked formations.

Nevertheless, as with Turkey, the Islamic State logically at some future point would attack Iran. The Islamic State’s goal is to reign over the entire Muslim world of believers, the umma, in a Sunni caliphate centered on Sunni beliefs and Sunni interpretations of the Koran. Iranian society is Persian and overwhelmingly Shiite; Turkey is Sunni, but comprises mainly Turkic peoples, along with a Kurdish minority accounting for 15 percent of the population.

One must also eventually consider nuclear proliferation issues, and question the Islamic State’s relation to the nuclearization of the Middle East. Would an ambitious Islamic State not require nuclear weapons to face Iran (and Saudi Arabia)? What would the United States and Israel do if it began to pursue them?