Editor's Note: The operation to recapture the key northern Iraqi city of Mosul from the Islamic State is now underway. Attempts to build up the necessary forces and pave the way for the attack have taken more than a year. The operation is expected to go on for months, if all goes according to plan. What we are seeing now is the initial advance onto the city itself, which will be followed by the fight to actually penetrate the Islamic State's defenses. Arguably the most important aspect of the operation is what happens after the city falls. Mosul fits into our overall coverage of the Iraq-Syria battlespace, but because of the size and nature of the combined operation, we will track it independently in this space.