As the United States and its allies look to fight the Islamic State in Iraq and Syria, longtime adversaries with a common fear of the radical movement are scrambling to see if they can cooperate to defeat the rising threat.
The jihadist group known as ISIS has so far thrived in part because its enemies are also enemies of one another, a reality that has complicated efforts to muster a strong response to its rampage. That factor has been a crucial consideration in war planning in capitals as diverse as Tehran and Washington, London and Damascus. But the potential threat has also forced a re-examination of centuries old tensions between Sunnis and Shiites, Kurds and Turks.
“Everyone sees ISIS as a short-term nemesis,” said Vali Nasr, a former senior adviser at the State Department who is dean of the School of Advanced International Studies of Johns Hopkins University, adding that ISIS had thrust the region’s traditional set of rivalries into a “momentary pause.”
When the United States military was preparing to leave Iraq in 2011, its primary enemies were, for example, three Shiite militias, managed by Iran’s spymaster, Qassim Suleimani, and armed with bombs traced to factories in Iran. But recently, as United States warplanes bombed ISIS fighters closing in on an Iraqi town, Amerli, Mr. Suleimani directed three militias fighting the same enemy on the ground.