The Islamic State forced the world to take notice when the extremist group overran Mosul, the second largest city in Iraq, in June 2014.
Just months earlier, President Obama had described ISIS as “the JV team.” But by August of 2014, the U.S. was bombing ISIS in Iraq, and early Monday, the U.S. teamed up with the Iraqi army and other allies in a major offensive to recapture the northern Iraqi city.
If the Islamic State’s capture of Mosul marked the high point of the group’s expansion, its expulsion would mark a major setback for a group that’s steadily been losing territory in Iraq and Syria.
Here are five key things to look for as the battle for Mosul plays out:
1. Mosul is the last Iraqi city held by ISIS: ISIS has already been driven out of other important Iraqi cities, such as Fallujah and Ramadi in the west. But it took weeks of intense street battles.
Based on this experience, the Iraqis are not planning to storm Mosul and all signs point to a campaign expected to proceed at a measured pace. The main Iraqi forces are 20 to 30 miles outside the city, as NPR’s Alice Fordham reports from Erbil.
But if defeated, ISIS will not longer control any large population centers in Iraq, and will be reduced to a rural insurgency concentrated mostly in western Iraq. Whatever happens in Iraq, though, the Islamic State will still have a strong presence in Syria, including the desert city of Raqqa, its de facto capital.
The Iraqi army, backed by U.S. air power and other allies, launched an offensive Monday to retake Mosul from the Islamic State.
2. ISIS declared the caliphate in Mosul: ISIS leader Abu Bakr al-Baghdadi declared the caliphate, or Islamic state, at the Grand Mosque in Mosul shortly after the group took the city. The Islamic State was on a roll at the time, surging across Iraq at the time as the Iraqi army collapsed in one city after another.
The capture of Mosul demonstrated the confidence of ISIS at the time and the threat it posed to all of Iraq and the wider region. In contrast, losing Mosul now would be a huge blow strategically and symbolically for the group. ISIS would be in retreat and would have a much harder time selling the idea of a caliphate if it lost the city where it was declared.
3. A stepped up U.S. air campaign: The U.S. bombing campaign, now a little more than two years old, has been limited. One reason is the difficulty of identifying and striking small, isolated groups of ISIS fighters in densely populated urban areas.