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Policy Analysis

PolicyWatch 2273

ISIS, Iraq, and the War in Syria: Military Outlook

Jeffrey White

Also available in العربية

June 19, 2014

Events on the battlefield will reveal the true effects of the crisis, but the ISIS campaign in Iraq could ultimately help the Syrian opposition and hurt the Assad regime.

The stunning advance of the Islamic State of Iraq and al-Sham (ISIS) in northern and western Iraq over the past week has significant military implications for the war in Syria. The jihadist group's forces and operations in Syria have already been affected positively and negatively by its commitments in Iraq. Going forward, Syrian rebel factions may take advantage of the ISIS campaign in Iraq to move against the group's positions in Syria, especially in Raqqa province. They may also be able to capitalize on the withdrawal of Iraqi Shiite militants who had previously been fighting on behalf of the Assad regime. For the regime, the situation will require more effort by its native forces and perhaps by its Hezbollah ally, which may need to pick up the slack caused by the departure of Iraqi elements. Bashar al-Assad's forces may have increased military operations against ISIS since the latest crisis emerged, putting further pressure on the regime's limited and stretched military assets.

If, as seems likely, the fighting in Iraq continues at serious levels for some time, these effects will become more pronounced in Syria. But developments on the battlefield in both countries will provide the clearest indicators of who is benefitting from the situation and who is not.


Earlier this month, ISIS forces began a rapid advance in northern Iraq, routing government forces and taking the important city of Mosul by a coup de main. Facing almost no resistance and supported by disaffected Iraqi Sunnis, ISIS continued its drive south, overrunning Iraqi military facilities, taking additional towns, threatening Samarra and Baquba, and arriving within thirty-seven miles of Baghdad itself. Stiffening government resistance slowed the advance, as did the mobilization of Shiite militia forces and volunteers, Iraqis returning from Syria, and, reportedly, Iranian forces. Meanwhile, Kurdish forces have secured the northern city of Kirkuk and prevented ISIS penetration into the Kurdistan Regional Government.

With a force estimated to number a few thousand, ISIS was able to bring Iraq to the brink of collapse, defeat major army formations, capture large amounts of military equipment, loot hundreds of millions of dollars from Iraqi banks, and begin establishing itself as the governing authority across a large tract of Sunni territory. The group did not do this alone, cooperating with Sunni tribal forces and former Baathists of the Saddam Hussein regime. While the ISIS advance has slowed, it has not come to a halt -- rather, it has created a new reality in Iraq, and its implications for various actors in Syria are becoming apparent.


The ISIS campaign in Iraq will likely prove to be a mixed blessing for the organization in Syria. To be sure, the positive effects for its forces may be manifold. In the near term, ISIS as a whole will be politically and psychologically strengthened. It will be seen as successful in battle, capable of major organizational and logistical accomplishments, and clever and supple in its operations. The group's image as an irresistible force will be enhanced, and those living in ISIS-controlled areas will see little prospect of relief from its rule.

ISIS will also benefit from the very large amounts of cash looted from Iraqi banks, reportedly as much as $495 million. This sum will enhance the group's ability to build its forces, arm them, and provide governance, goods, and services within its area of control.

Perhaps most important, ISIS military capabilities could be significantly boosted by the capture of large numbers of Iraqi army vehicles, weapons, and ammunition, as well as by the addition of new recruits. At minimum, these gains will allow the group to arm and equip more fighters, enhance its mobility, and increase its firepower. This assumes that ISIS is capable of recovering, integrating, and maintaining the captured equipment. New videos have shown the movement of such equipment into Syria, and ISIS units in Iraq are already employing captured Humvees and trucks; they could potentially employ captured tanks and artillery as well. The effects of these developments may soon be felt in Syria.

Yet the Iraq campaign will likely have negative effects for ISIS forces in Syria as well. First is the potential diversion of forces. It is not clear what percentage of ISIS forces are fighting in Iraq, but it is believed to be half or more of the group's roughly 10,000 members. ISIS may be compelled to commit even more forces to Iraq, weakening its military position in Syria. Second, the large amount of Iraqi territory over which the group has gained at least nominal control might also require additional forces from Syria, both to resist government countermeasures and help control the areas. Third, the Assad regime has reportedly increased its military operations against ISIS, apparently in response to the group's movement of captured military equipment into Syria, and perhaps in coordination with the Iraqi government. On June 15-16, regime air forces struck ISIS-associated targets in Raqqa and Hasaka provinces. If such strikes become a regular occurrence, they will put additional pressure on ISIS and perhaps weaken its ability to fight in Syria.


ISIS now faces a potential three-front war: against various Syrian rebel factions, against Iraqi government forces, and perhaps against the Assad regime, which had largely refrained from directly confronting the group until recently. This situation will likely prevent ISIS from concentrating its resources against its Syrian opponents and should give these enemies opportunities to move against it. The group's ability to defend its territory in Raqqa and Aleppo provinces appears to have weakened recently, and rebels have been able to take some advantage of this. At the same time, the ISIS offensive in Deir al-Zour province has at least slowed, relieving some of the pressure on its Islamist opponents in the area.

The return of Iraqi fighters from Syria to Iraq should also benefit the rebels. Iraqi Shiite militants have been heavily involved in the fighting around Damascus and Aleppo, and their departure has weakened the effective coalition of forces the regime has used to score victories. These effects would be compounded if Hezbollah or Iranian forces serving in Syria were sent to Iraq. Hezbollah leader Hassan Nasrallah has indicated that his organization will assist in Iraq if asked, though the group seems more likely to increase its commitment in Syria instead.

Whatever the case, the departure of some allied forces will increase the burden on the regime's regular and irregular native forces, which are already stretched thin and suffering substantial casualties. Hezbollah is already said to be making up some of the deficit, but its existing forces in Syria continue to take casualties, and its commitment to Assad remains a political problem at home in Lebanon. Moreover, if the reported airstrikes against ISIS in eastern Syria become a persistent mission, the regime's limited air assets will be diverted from attacking the opposition in more strategically important parts of the country, giving some relief to rebel forces and civilians.


The escalated fighting in Iraq will likely continue for some time. Now that the initial ISIS advance has slowed, neither the group nor the Iraqi government has the capacity to quickly or radically change the situation on the battlefield. The fighting is likely to be protracted and indecisive, with similar effects on the situation in Syria.

Over time, an ongoing battle of attrition in Iraq may work to the advantage of rebel forces in Syria. While ISIS is well organized and formidable in some respects, maintaining a two- or three-front war will require it to allocate resources against multiple threats, replace combat losses, integrate captured equipment, consolidate its hold on newly gained areas, and stave off Iraqi counteroffensives and opportunistic advances by its enemies in Syria. For an organization of its size, this adds up to a serious challenge.

In Syria, it is unclear to what extent the rebels can take advantage of the situation. Opportunities could arise to make gains against ISIS and the regime, but the rebels' ability to exploit them is uncertain. Their weaknesses in command likely mean that any such response would be ad hoc and depend on existing or newly formed coalitions of rebel units. This would reduce the prospect for major success against their enemies.

For the Assad regime, the Iraq situation is yet another major challenge. Damascus will need to find a way to compensate for the loss of allied Iraqi militants and perhaps intensify the fight against ISIS in areas where regime forces are weak. Furthermore, any success it has against ISIS would actually help the Syrian opposition.

Again, events on the battlefield will clarify the true effects of the crisis. If ISIS becomes involved in a protracted war of attrition in Iraq, its position in Syria could weaken visibly. Rebel successes or failures against the Assad regime will indicate whether or not they have been able to take advantage of the situation. Likewise, further regime victories against the rebels and an increase in Hezbollah forces would indicate that Assad is overcoming the negative effects of the crisis. There will be plenty of conflicting claims about all of this, but the facts on the ground should become clear.

Finally, while the ISIS advance in Iraq has increased the complexity of the Syrian war, it also presents another opportunity for the United States and its allies to make gains against Assad. Military assistance to moderate Syrian rebel groups would help them take advantage of the situation, allowing them to act more effectively against ISIS, the enemy of all, and the regime, the enemy of most. Given that ISIS-seized American military equipment could soon affect the group's capabilities in Syria, the rebels may need concrete U.S. assistance now more than ever.

Jeffrey White is a defense fellow with The Washington Institute and a former senior defense intelligence officer.