Kurds, who live in both Syria and Iraq, are mostly Sunnis, but they’re ethnically distinct from Arabs. They control a swath of northeast Iraq where a lot of the oil fields lie. Early in the conflict, they were relatively uninvolved. But when ISIS pushed into Kurdish territory in August 2014, the Kurds struck back and have played a significant part in ISIS’s defeats since.
Iraqi Kurdistan is governed semi-autonomously. The Kurdish security forces are partly integrated with the government, but there are somewhere between 80,000 and 240,000 Kurdish peshmerga (militias) that don’t answer to Baghdad. They’re well equipped and trained, and represent a serious military threat to ISIS.
The early crisis allowed Kurds to expand their territory of control at the government’s expense. The Kurds took advantage of the chaos to occupy Kirkuk, a city near massive oil deposits that they’ve wanted for some time. That means the crisis was, in a strange way, a boon to the Kurds. ”This crisis is a lifeline for the Kurds,” Iraqi politics expert Kirk Sowell said at the time.
But in August, ISIS launched a big push into Kurdish territory, which dramatically altered the course of the conflict. By August 7, ISIS forces had occupied several strategically valuable towns and were ”minutes” from the Kurdish capital Erbil, where a number of American advisers were based.
This threat committed the peshmerga to the fight against ISIS. Moreover, it helped pull the US into the war: The threat to American personnel in the Kurdish capital, Erbil, was one of the key factors that initially prompted American intervention against ISIS.
Since then, it’s become clear that ISIS’s incursion into Kurdistan backfired. The Kurds pushed ISIS out of their territory, and Kurdish forces have played a key role in rolling back some of ISIS’s gains across northern Iraq (for instance, the Mosul Dam and the strategically important town of Sinjar) with significant US support.