ISIS’s major breakthrough was a victory in Mosul, a northern Iraqi city and the country’s second most populous, in June 2014. Immediately after that, it made rapid advances, as this New York Times map of ISIS’s progress details:
Combine that with ISIS territory in Syria, and it controls a snaking band of territorythat’s about the size of the United Kingdom. This updated map from the Institute for the Study of War is very clear; ISIS-controlled territory is in black, and ISIS has some military capability in the red areas and some room to operate in the pale red areas:
However, ISIS has lost significant amounts of territory in Iraq. The most important such victory was in April, when the Iraqi army and Shia militias pushed ISIS out of Tikrit, Saddam Hussein’s hometown and a major Sunni city. Now many Iraq experts think the group is on the road to losing control of all of its Iraqi possessions.
ISIS “will lose its battle to hold territory in Iraq. It may well take one to two years to reduce their defenses in cities like Mosul, Tikrit, and Fallujah, but the ultimate outcome is no longer in serious doubt,” Douglas Ollivant, the National Security Council director for Iraq from 2008 to 2009 and current managing partner at Mantid International, wrote in February.
This may take quite some time. In May, ISIS struck back by taking Ramadi, the provincial capital of Anbar province, indicating that it is very far from fully defeated. But in the long run, the trajectory for ISIS in Iraq is very grim.