A bloody past and centuries of mistrust between two branches of Islam are threatening to derail Iraq's bid to crush ISIS — as well as the American war plan.
The rise of Iran-backed Shiite militias battling the extremists has left the country's Sunni minority wondering what to do next.
The so-called Popular Mobilization Units made up primarily of Shiites aligned with Tehran have taken on a kind of semi-official status in Iraq's security forces, fighting at the tip of the spear during recent anti-ISIS campaigns in the cities of Tikrit and Ramadi. In some cases, they are led by men accused by the U.S. of being responsible for attacks on Americans.
But Sunni fighters are expressing dismay at the idea of being stationed with Shiites, even if both parties share a common enemy in ISIS.
"I will not fight with the Hashad," one Sunni tribal fighter said in an interview with NBC News, using the Arabic name for the Popular Mobilization Units. "They … take their orders from Iran. It's a shame on me if I fight next to an Iranian."
An eight-year war between Iraq and Iran in the 1980s left at least 500,000 people dead. Sectarian violence between Sunnis and Shiites in the years following the 2003 U.S. invasion killed thousands more.
Until recently, U.S. training in Iraq has focused on Shiite and Kurdish fighters battling ISIS. But the White House last month announced that 450 military trainers would be sent to Anbar province to work with Sunni tribes that feel displaced by the Shiite-led government and have not joined the fight against ISIS enthusiastically. The Sunnis are being trained at Taqqadum air base — alongside what the Pentagon describes as a "low double digit" number of Shiites serving as liaisons between militia units and the Iraqi government.