The Iranian government is Shia, and it has close ties with the Iraqi government. Much like in Syria, Iran doesn’t want Sunni Islamist rebels to topple a friendly Shia government. So in both countries, Iran has gone to war.
Iran has been involved in at least three ways. First, and perhaps most importantly, Iran is the big backer behind Iraq’s Shia militias, a major force in the battle against ISIS. ”Let’s call a spade a spade here: The Iranians are running the show,” Phillip Smyth, a University of Maryland researcher whose work focuses on Shia militias, explained in March. Iran arms many of the groups; Qassem Suleimani, the commander of Iran’s elite Quds Force, is often said to be leading the overall militia strategy.
Suleimani’s role actually may be broader than just directing militia strategy. A number of outlets have reported that he’s playing a critical role in shaping Iraq’s overall strategy in the fight against ISIS, one going so far as to call him the country’s ”chief tactician.” This strategic guidance is Iran’s second major contribution to the ISIS fight — and one that indicates just how deeply enmeshed Iranians are in Iraqi politics.
Finally, there’s Iran’s direct military involvement. Iran has openly conducted airstrikes on ISIS targets in Iraq, but usually denies that it has deployed any troops on the ground. That’s a little hard to believe given Suleimani’s role in the conflict: It’s very hard to imagine the leader of the Quds Force is traveling without any accompaniment from Quds Force soldiers. And there have been numerous (unconfirmed) reports of Iranian troops fighting on the ground.
So Iran’s involvement in the conflict is extensive. This creates something of a dilemma for the United States, which, in an ideal world, wants to limit Iranian influence in Iraq as much as possible.
Iranian involvement has played a critical role in helping beat back ISIS, but it’s also strengthened Iran’s political hand inside Iraq. That puts the United States in an awkward position of tacitly working with Iran against ISIS while nominally attempting to limit Iranian influence.