Because of the way its military advance in Iraq has played out, the Islamic State in Iraq and the Levant has earned prestige and a propaganda boost — it is viewed as a competent organization capable of decisive results. This growing perception will be crucial in the group's ability to attract a growing share of the foreign fighters heading toward the region, and possibly draw additional Syrian rebel fighters to its ranks. The group's seizure of weapons and vehicles — much of this equipment taken from retreating Iraqi soldiers — and reportedly more than $1 billion in funds during the recent Iraq offensive will only increase its attractiveness to jihadist fighters.
The equipment taken includes armored vehicles, small arms, ammunition, artillery, communication devices, uniforms and logistical vehicles. The Islamic State in Iraq and the Levant may have also seized night vision equipment and air defense weaponry. This gear would provide a substantial boost on the battlefield in Syria, and the group has indeed already begun to transfer some of this equipment across the border.
The growth in the Islamic State in Iraq and the Levant's prestige could in theory have detrimental effects on the rebels and on the Syrian regime. Since the transnational jihadists serve the cause of neither, their efforts in Iraq will create a mixed set of variables for the combatants in Syria.
Effects on the Syrian Regime
Perhaps the greatest negative consequence for the regime of Syrian President Bashar al Assad is the shift of Iraqi Shiite militants back to their homeland to confront a resurgent Sunni opposition. The Syrian regime has come to rely heavily on foreign fighters — be they Hezbollah combatants, Islamic Revolutionary Guard Corps advisers or Shiite volunteers from across the region — to bolster its ranks and negate its demographic disadvantage. These foreign fighters, most notably the Hezbollah members, played a critical role in halting the string of defeats that beset the regime in late 2012, and they continue to spearhead regime offensives across Syria. Furthermore, and unlike what has happened with the Syrian rebels, the regime has not suffered from divisive infighting due to the influx of foreign fighters.
With the Islamic State in Iraq and the Levant and its allies advancing south toward Baghdad from Mosul, and with sectarian emotions flaring across the region, Iraqi Shiite fighters are keen to return to their homeland — they have made this desire abundantly clear in statements and videos. Even Hezbollah has threatened to dispatch fighters to Iraq. Though Hezbollah is unlikely to shift much of its efforts from Syria to Iraq — partly for logistical reasons, but mostly due to the regime's critical dependence on the group — it will probably move additional fighters to Syria to help offset losses of Iraqi militia. There is already substantial evidence that thousands of Iraqi Shiite fighters are on their way home. Iraqi fighters have reportedly withdrawn from Syrian fronts in the coastal province of Latakia and in al-Meliha, in the suburbs of Damascus, while witnesses have reported seeing convoys of trucks leaving the football stadium that served as the Iraqi militia base in the northern city of Aleppo.
The Islamic State in Iraq and the Levant's current focus on Iraq has also wrought a notable decline in the intensity of rebel infighting. In the months prior to the fall of Mosul, rebel infighting in Deir el-Zour province in particular resulted in hundreds of rebel casualties as Jabhat al-Nusra and its rebel allies battled against Islamic State in Iraq and the Levant fighters. Though these clashes continue, particularly in Aleppo and Deir el-Zour provinces, the intensity of the fighting has markedly decreased, a clear sign that the Islamic State in Iraq and the Levant has turned its attention, and likely a large number of its fighters, to Iraq. It could always move its forces back across the unrecognized border, but for now, the group appears to be prioritizing Iraq and will likely keep reinforcing its fight there against Iraqi government counteroffensives.
Effects on Syrian Rebels
The Islamic State in Iraq and the Levant's shift in focus to Iraq will probably help Syrian rebels more than the regime. For one thing, the Islamic State in Iraq and the Levant over the last year has maintained positions mostly in northeastern and eastern Syria, where the loyalist presence was rather scant and certainly not as critical as areas farther to the west. This geographic distribution in part reflected the militant group's opportunistic behavior, seizing lightly held territory, and its desire to secure energy resources, and it meant that the Islamic State in Iraq and the Levant was primarily a threat to Syrian rebels and to Kurdish militias in Hasakah.
However, Washington and its allies will be increasingly nervous about supplying advanced weaponry to the rebels in Syria. Having shown it can seize weaponry from the Iraqi army, the Islamic State in Iraq and the Levant's potential ability to seize weapons delivered by the United States to often ragtag rebel groups worries the Americans. This re-evaluation comes at a particularly bad time for the rebels, who seemed on the verge of finally convincing the United States and other allies to deliver substantially more weapons to their fighters.
Interestingly, while the regime preferred not to interrupt its enemies' infighting, it undertook a notable aerial bombing campaign against the Islamic State in Iraq and the Levant, both within Syria and across the border in Iraq, after the fall of Mosul. Two things can explain this turn of events. First and less important, the regime may sense an opportunity to strike at the Islamic State in Iraq and the Levant and relieve pressure on regime forces that come into contact with the militant rebels — particularly the 17th division in Raqqa province — while the group is busy in Iraq. The primary reason, however, is the regime's need to demonstrate that it is invested in the well-being of its allies, and in particular that it is attuned to the concerns of its patron, Iran. With the Islamic State in Iraq and the Levant becoming a major threat to Baghdad, Hezbollah and Tehran's interests in Iraq, the Syrian regime will try to show that it is doing its part in the wider struggle. The al Assad regime can leverage an opportunity to share intelligence with others, since the Islamic State in Iraq and the Levant is now the prevalent regional threat.
It is clear that the fall of Mosul and the spike in the fighting in Iraq have further complicated an already elaborate regional conflict where borders are fast losing their importance. For the Syrian battle space, the developments in Iraq bring a mixed array of advantages and disadvantages to the varying combatants. Even if it does not decisively tilt the battle, the Islamic State in Iraq and the Levant's Iraq pivot will play an important role in the conflict in Syria.