Twenty-two months ago, ISIS seized Mosul, Iraq’s second largest city, during a blitzkrieg across the region. The militants have held it ever since. At last, an offensive to retake the city has begun. The stakes could not be higher; the operation will biggest test yet for Iraqi forces and Barack Obama’s counter-ISIS strategy, and victory will not come easy.

The Iraqi Army, which is backed by U.S.-led coalition intelligence, advisers and fire support, made its first moves to capture villages south of Mosul in an attempt to begin to block off enemy access and to fortify supply routes heading north towards the sprawling city. These first moves are essential in preparing for an actual assault into the city itself, which is still likely many months away.

Like , the operation was launched from what is emerging as the region’s premier coaliton forward operating and command and control base in the village of Makhmour. This site is known as the Nineveh Operations Center and is known to include a Marine artillery fire base nearby.

The existence of a previously unknown Marine fire base in northern Iraq came suddenly to light last

During these initial missions, the Iraqi Army raided several villages northwest of Makhmour, raising the Iraqi national flag after clearing out ISIS combatants. Similar operations will likely follow as coalition forces begin to slowly fortify the roughly 65 mile essential supply route along the Tigris river into Mosul.

Clearing villages nearby a major fortified outpost is a far cry from taking down a sprawling urban metropolis that is crawling with hardened ISIS fighters. Such an operation takes, above all else, tremendous amounts of well-trained manpower, and this is something that the Iraqi Army still lacks.

Army Col. Steven Warren, a spokesperson for the U.S. led anti-ISIS coalition, that it would require roughly eight trained brigades of about 3,000 Iraqi soldiers each to take the city ( put the number at 36,000 troops.) The operative term being trained.

The quality of Iraq’s forces, even after well over a decade of constant training, is still inconsistent at best. As such, 24,000 well trained soldiers that will actually stand their ground during intense and bloody urban warfare is something that Iraq’s Army may not have anytime in the near future.

The, a much smaller city with a largely vacated population, used just a fraction of the strength required to take back Mosul, a place where many hundreds of thousands of civilians still reside. Additionally, with so many civilians still living in Mosul, the use of air power will be far more restricted than it was in Ramadi.

There is thoughtand 5,000 Iraqi troops now deployed in and around the Nineveh Operations Center. Clearly this is nowhere near the number needed to start looking toward Mosul as a realistic objective.

Defense Intelligence Agency chief Lt. Gen. Vincent Stewart showed little confidence in the possibility of Mosul being fully liberated in 2016

“Mosul will be a complex operation. I’m not as optimistic that we’ll be able to turn that in the near term, in my view, certainly not this year. We may be able to begin the campaign, do some isolation operations around Mosul, but securing or taking Mosul is an extensive operation and not something I see in the next year or so.”

With all this in mind, it is likely that what we will see is a long, creeping offensive that will culminate, many months from now, in a partial encircling of Mosul in what will likely be a classic “” operation.

Enemy forces will not be able to flee the city en masse aside to the south or east or west. Just the northerly routes will be left un-flanked. These routes can be blockaded with checkpoints or attacked via air power, leaving fighters with nowhere to run without being confronted militarily.

As Iraqi forces push north through the city, ISIS fighters will also be pushed in that direction. In the end the Islamic State’s control of Mosul would reach an end, but it is likely to be an incredibly bloody and costly affair.

It is this dire forecast that is most concerning, regardless of whatever troop levels the Iraqi government can supply. Will Iraqi troops stick it out through what will likely be some of the most intense, complex and sustained urban warfare experienced in modern times? So much is riding on the answer to this question. Just two years ago, Iraqi security forces largely deserted Mosul in the face of confronting comparatively few ISIS fighters.

A decisive victory, no matter what the costs, in Mosul would be a massive boost to Iraq’s military, as well as to much needed nationalist sentiments. A retreat would result in the exact opposite and could have catastrophic political results in an already fractured country as well.

The stakes are similar for both ISIS and the White House. If Mosul is liberated it would be a sign thatmay have merit. For ISIS it would signal a massive defeat as losing geographically territory, and especially a huge prize like Mosul, strikes directly at the heart of their claim of an expansive caliphate.

U.S. Secretary of Defense Ashton Carter seems to get the reality that the so-called “coalition” of…

Either way, the ball has started rolling. Where it will land exactly remains anyone’s guess.