Once Mosul is recaptured from ISIS, what then?: Brian Stewart

Military offensives to recapture cities from a dug-in enemy are always perilous, but the campaign to free Mosul from ISIS is one for the books a tactical nightmare placed on top of an active political volcano.

The extraordinary complexities of Iraq are such we can't say with confidence if it will be possible to defeat ISIS within a matter of weeks or if it will take a debilitating siege of many months, perhaps accompanied by a massive humanitarian disaster and a whole new wave of political and sectarian crises over what comes next.

Even the military equations are hard to pin down. Mosul is an immense battle zone Iraq's second largest city that housed two and a half million before the war being contested by a surprisingly small number of forces: perhaps 30,000 assembled on the government side, and no more than an estimated 3,000-5,000 ISIS fighters.

• Kurdish forces retake Iraqi villages outside Mosul
• Canadian troops supporting Kurds in fight to free Mosul from ISIS

Such slim numbers make it hard to predict the course of fighting.

As it is, few would have predicted last spring that the Mosul operation could happen at all this year, as Iraq's humiliated and largely shattered army was still deeply demoralized and fragmented.

It was only two years ago, after all, that the world saw the army break and run before the historic ISIS surge southward into Iraq, an advance that ultimately allowed ISIS to advance and quickly take over vast swathes of both Iraq and Syria for its proclaimed caliphate.

Such a debacle is hard for any army to recover from.

Momentum has shifted

That said, the momentum of war there has actually been running strongly against the jihadists for much of this year, as they've been driven from most of the territory they seized and now are struggling, backs to the wall, to hold onto their last key city in Iraq, Mosul.

That's because for all its daring and brutality, ISIS, which rarely numbered more than 30,000 fighters inside Iraq at any time, really had no chance to hold all the ground they'd captured.

Iraq's geography was unforgiving, with little natural cover in a large, flat countryside, meaning ISIS could not manoeuvre in strength in the open without inviting attacks by bombs, missiles and drones.

It was forced to retreat mainly into urban areas, where fellow Sunnis, hostile to the Shia-dominated Iraqi government, were in many cases at least initially supportive of ISIS and provided cover in the form of a large civilian population, restricting the coalition's ability to bomb.

That's when the scales shifted to favour Iraq, for this retreat into urban havens gave the government what was desperately needed time to rebuild that humiliated army under allied guidance.

Simultaneously this time allowed Kurds in eastern Iraq with Canadian and other allied help to build up their own forces that are highly effective against ISIS.

And it wasn't long before ISIS became increasingly incapable of even holding onto those urban areas, no matter how extensively they fortified them with tunnels, trenches, dugouts and all manner of booby traps.

Tikrit, Ramadi, Fallujah one important city after another fell to Iraqi offences heavily backed up by air and artillery support in what became the slow and grisly proving grounds for the Mosul showdown.

There's no ignoring the fact, however, that the Iraqi army units assembled for the Mosul attack are still very uneven. The elite counterterrorism units selected to handle the toughest fighting are battle-weary after prolonged campaigns, while other units are untried.

Also gathered outside Mosul are separate Shia militia formations and Sunni tribal paramilitary groups, along with close to 5,000 Kurdish Peshmerga fighters advancing from the east.

• Iraqi city of Fallujah declared 'fully liberated' from ISIS
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There are hundreds of U.S. and allied advisers co-ordinating supporting fire and logistics, but such a mix of Iraqi units makes command and control by headquarters difficult. Shia militia, for example, are often backed by Iran; the Sunni units listen closely to Saudi Arabia; while Kurds are deeply suspicious of the central government in Baghdad.

Most worrisome, Shia militia have frequently been accused of atrocities against Sunnis in territory they've taken, so there's international pressure on Iraq to keep them out of Mosul proper. The final push, when it comes, is expected to be carried out by the army, special forces and Sunni paramilitary police units.

Kurdish soldiers in huge firefight with ISIS near Mosul, Iraq

8 years ago

Duration 1:07

Video captures chaotic, frenzied battle

Humanitarian crisis looms

The potential for humanitarian crisis is obvious in a city where the remaining 1.2 million civilians are so terrified, the government is pleading with them to stay inside their homes as fighting goes on. Many aid groups fear hundreds of thousands will even risk ISIS reprisals to flee, further swamping overburdened refugee camps.

The biggest question of all, perhaps, is whether ISIS will really go down fighting in government buildings and the maze of streets in the old city, or instead escape to a still-open route to the north, towards Syria and ISIS units there. Some commanders would even favour letting them go without hindrance; others demand no let-up.

Despite months of planning, this seems very much a battle without clear focus, except for the wish to clear the city of ISIS, which in turn indicates that the vital political question of what happens in Iraq after Mosul is finally won is nowhere near being answered.