Mosul, Iraq’s second-largest city, emerged as a future battleground in the summer of 2014, when a small number of Islamic State, also known as ISIS or ISIL, fighters (perhaps 1,500–2,000) took control of the municipality. The Iraqi combat units responsible for countering ISIS fled, abandoned their equipment (including heavy weapons) and left the field to the jihadists, who rapidly consolidated their presence and assumed administrative responsibility for the city.
The suddenness and comprehensiveness of the ISIS victory underscored the fundamental incapacity of the Iraqi state and the possibility that ISIS might actually consolidate the ‘caliphate’ it had declared in June 2014, both of which threatened the legitimacy of Iraq’s new government under Prime Minister Haider al-Abadi. While Abadi enjoyed nearly universal foreign support, stemming from deep frustration with his predecessor Nuri al-Maliki’s mix of authoritarianism and sectarianism, Maliki’s domestic popularity remained fairly solid. This hobbled Abadi’s efforts to gain traction and left him politically highly vulnerable in the wake of the Iraqi forces’ debacle at Mosul.
Thus, the looming battle for Mosul had as much political importance as it had military importance for both sides, which made it all the more inevitable. Accordingly, it soaked up an inordinate proportion of the combatants’ resources. The battle began in October 2016 and is ongoing, though it is now clear that Iraq-led forces will defeat ISIS in Mosul and retake the city.