The offensive by Iraq to retake Mosul from ISIL is considered a pivotal moment in defeating the group. The city has been the group's de facto capital in the country since mid-2014.

In June 2014, ISIL seized the key trading city, which is near the borders of Syria and Turkey. It is also located near vital oil fields and pipelines.

Retaking Mosul would limit the movement of ISIL fighters, weapons and supplies. Securing the oil fields will also hit ISIL's finances hard. ISIL operations are partly funded by illegal oil sales. Retaking Mosul means removing the militant group's last bastion of power in Iraq.