By Anthony Cordesman, Center for International and Strategic Studies–

The fight to liberate Mosul has begun. In fact, it began with a new round of U.S.-led air strikes before the Iraqi announcement that the various elements of Iraqi ground forces were ready to engage. It will be one of the most critical elements of the U.S. military effort to defeat terrorism and violent Islamist extremism, as well as help determine the success of future U.S. efforts to bring some elements of stability to an increasingly more unstable Middle East.

There is no way to know how hard the fight will be or how determined ISIS is to hold the city. Estimates of its force size are surprisingly low, and rarely exceed 4,500 actual fighters. At the same time, it has had months to prepare, and has shown all too clearly how willing it is to sacrifice its fighters in suicide attacks and battle of attrition when it chooses to do so. It is also all too willing to use civilians as shields and tools of war. It also has to consider how easily it can hold its positions in Syria, and retain the loyalty of its fighters if it does not turn Mosul into as long a battle as possible. Falling back does not offer much security given its loss of any secure route through Turkey, and a successful Iraqi advance that includes both Mosul and the rest of Ninewa will further contain any ability to get new volunteers, money, and supplies.

At the same time, “winning” in Mosul is likely to be highly relative and presents major challenges in terms of Iraqi unity. All the various elements of Iraqi forces have different goals and objectives. This is why the United States has already spent so much time quietly persuading the Kurds to help without trying to acquire new territory, pushing Iraqi central government forces to take over the main military effort, creating at least some local Sunni militia elements and limiting the role of the Shi’ite militias. Iraq’s central government and the United States face almost as much of a threat from their “allies” as from ISIS—keeping them from turning on each other and from trying to exploit the victory over ISIS to their own advantage at the expense of Iraqi unity is at best going to be a “close run thing.”

Every major faction involved in fighting ISIS has its own priorities and conflicting goals. The former Sunni governor of Ninewa—the province of which Mosul is part—wants to make it an Arab Sunni enclave. The Kurds—which are divided against each other—have their own ambitions and talk about independence. The Iraqi Army remains weak and uncertain, and the police are all too ineffective and divided along sectarian and tribal lines. Some of the Shi’ite militias have mistreated Sunni Arab civilians in past operations and are extremists in their own right.

Some aspects of the fighting will be grim regardless of how well the forces involved are prepared and how willing they are to cooperate. It is possible that ISIS will collapse under pressure, but more probable that Mosul will be the scene of another human tragedy in the Iraq-Syria conflict—either in terms of the actual fighting or the long aftermath needed for rebuilding and recovery. ISIS already has had months to turn Mosul into a fortress of booby traps and bombs, and to work out a strategy for using human shields and exploiting the population. Iraq has few surplus civil resources and limited capacity to manage them.

It is also clear that preparations to deal with the civil and human impact of the fighting may not be adequate and cannot be made so. There simply are too many conflicting factional tensions, and too many limits to the civil options involved if anything like the worst-case estimates of displaced persons, collateral damage, and mistreatment of civilians take place. About all that can be done is to be honest in addressing such problems, and provide the best aid options possible. War remains hell, and efforts to describe the “revolution in military affairs” as a way of minimizing its human impact do more to discredit than disguise.

The Iraqi government is also a potential “threat.” It has good leadership at the very top in prime minister Abadi, but the bulk of the civil government remains corrupt, self-seeking, and deeply divided. Its ability to deal with a million or more civilians caught up in the fighting or displaced from their homes is uncertain at best. Far too often, its reaction to a military victory is to appear, make dramatic promises, and then fail to act.

In the case of Mosul, such a failure could drive large numbers of Sunni Arab civilians into Shi’ite or Kurdish areas that are already tense, effectively bankrupt because of low oil revenues, and that have little surplus housing or infrastructure capacity. This too could make sectarian and ethnic problems worse. The Abadi government and the United States must have considered this, but their capacity to cope seems uncertain, and the end result could be more sectarian and ethnic tension and fighting.

In fact, the most critical aspect of the battle may not be whether ISIS is defeated. It may be whether Iraq’s deeply divided factions can find some way to cooperate if they win. The alternative could be worse than ISIS: Sunni versus Shi’ite, Arab versus Kurd, and Turkey, Iran, outside Arab states, and Russia all competing to serve their own ends. “Winning” could all too easily divide Iraq on a lasting basis and/or turn into new forms of civil conflict. Here, it is useful to hear about the preparations for the fight. The problem is the lack of any credible public statements as to how the Iraqi and U.S. governments will react once ISIS is defeated.

Both the proper timing and actual success are critical. This battle cannot be safely politicized. Any major reversal in the fighting for Mosul will affect the future stability of every political element in Iraq, the future success of the U.S. effort to create effective Iraqi security forces, and global perceptions of the future of both ISIS and other violent Islamist movements. Here, a certain amount of trust in the U.S. military will be critical. If U.S. military briefings sometimes seem a bit vague, they should be. Focusing on play-by-play descriptions of progress and problems weakens Iraqi trust and U.S. influence, and provides far too much information to ISIS.

At the same time, real success during the remaining months of this year can be of great value if it is possible to ensure such success. First, the success of the Abadi regime in moderating and unifying Iraqi politics and Iraq as a nation depends on success in both defeating Mosul and showing that the government will do its best to aid Mosul’s civilians.

Mosul is the only major population center in the Sunni Arab areas west of Baghdad. The fight in Anbar has only affected a tiny portion of the population. If the central government can lead the fight in Mosul and show it cares about the security and future of Iraq’s Arab Sunnis—while avoiding any further clash or tension with the Kurds—it will have enhanced its credibility and status as a central government.

Second, this kind of success in Mosul and Iraq will do much to restore U.S. credibility and influence. It will help counterbalance Russian success in Syria, limit the role of Iran, and restore some degree of confidence on the part of our other Arab allies. There are only bad “least bad” options left in Syria, and the human tragedy there is virtually certain to get much worse before it gets better.

The sooner ISIS fails in Iraq, however, the more vulnerable it will become in Syria—in terms of money, volunteers, morale, and credibility. If ISIS then fails in Syria as well, there may be at least some options to support Arab rebel forces than can really be trusted and help provide more humanitarian relief. In contrast, the longer ISIS has to prepare in Syria, the worse things are likely to get in eastern Syria—and Russia, Iraq, and Assad are almost certain to exploit this.

Third, regardless of who wins the coming U.S. election, the U.S. position will be far better off if the most critical battle in Iraq is already won. The case for civil aid to Iraq will then be far stronger, and U.S. influence and credibility in Iraq will be far stronger as well. The case for an active, meaningful partnership with moderate Arab states will be reinforced, and hopefully, the precedent of dealing with the civil outcome of Mosul will set a precedent for helping to deal with the human tragedy in Syria—an effort which now seems likely to only begin more than a year from now and require support for a decade or more.