As the Islamic State continues to lose ground in Iraq and Syria, one of the more common talking points for debate is the supposed prospect of an Iranian "land-route" running through Iraq and Syria to Lebanon and the Mediterranean, and what the U.S. response should be. But how seriously should the idea of the land-route be taken? If the land-route concept is taken seriously, what are the viable U.S. policy responses, if any?
When it comes to supporting clients and allies in Syria and Lebanon, Iran has relied on aircraft (mostly traveling to Damascus) and naval routes, both during and prior to the Syrian civil war even when a theoretical land-route passing through Iraq and Syria to Lebanon existed. Broadly speaking, the U.S. and its allies have been unable to prevent the use of aircraft and naval routes, and indeed there is little that can be done about those routes.
The prospect of a pure land route as an additional guarantee in the event of loss of access to all airbases and naval ports (which seems highly unlikely anyway) might sound attractive. However, using such a route as the primary means to move important supplies and weapons would have to take into account the problem of an Islamic State insurgency that will remain potent in the Syria-Iraq desert border areas even after the organization loses its formal territorial holdings. For the Islamic State, attacking Iranian military convoys using a land route through the Syria-Iraq border areas would be worthwhile for two reasons. First, the attacks would allow the group to bolster a propaganda message of fighting Iran. Second, the convoys could offer chances for seizing valuable war booty.
It is true that Iranian forces and Iranian-backed Shi'a militias (e.g. Hezbollah and multiple Iraqi groups) have been participating in the Syrian regime's broader offensive pushing eastwards towards the borders with Iraq. Yet this should not obscure the fact that the regime has its own vital reasons for pushing eastwards that tend to be ignored in favor of a simplistic view of the Syrian civil war as primarily proxy warfare between international powers. For instance, the regime wants to restore land trade routes with Iraq that existed before the war, and wants to reclaim the country's most valuable oil resources as well as important agricultural resources. Otherwise, the regime will face difficulties in trying to secure reconstruction and will be left too economically dependent on its allies Russia and Iran.
The leader of the 313 Force, a Syrian militia backed by Iran, poses in front of a sign with Bashar al-Assad's portrait that reads: "God willing, in the near future we can open the trade route between the two countries again" — an indication of the regime's intent to re-establish the trade route between Syria and Iraq.
For native Syrian militias fighting for the regime, there are reasons to want to push eastwards: for example, among those militias participating in the fighting are Sha'itat tribesmen with origins in the eastern Syrian province of Deir az-Zor. The Sha'itat tribe rose up in revolt against the Islamic State, which seized control of its areas in 2014, only to be brutally crushed. Now, many of those tribesmen who fled to regime-held areas are seeking to return home and exact revenge.
The Iraqi Shi'a militias in particular also have their own reasons for participating in the offensive. Their ideological allegiance to Iran and service to Iranian interests should not be denied, but participating in the fight to take eastern Syria is something they genuinely view as being in Iraq's interests by securing the borders and reducing the Islamic State threat. As Ja'afar al-Husseini, the military spokesman for the Iraqi Shi'a militia Kata'ib Hezbollah, explained to me: "Linking up [on both sides of the borders] secures the borders of Iraq, prevents the movement of the armed men [Islamic State] and helps to liberate the land of Syria, which is part of our belief that the battle is one in Iraq and Syria."
One may ask why the regime and its allies are only conducting these operations now. The most important point is that from the standpoint of the regime's immediate survival, the insurgency concentrated in the western half of the country posed by far the bigger threat than the Islamic State in the east. When the insurgency, led by jihadists and Salafists with CIA-backed groups functioning as auxiliaries, made major gains in the northwest of Syria by expelling the regime from all major towns in Idlib province in spring 2015, the regime lost a provincial capital (Idlib city) and was at risk of losing another one (Hama city), and faced the prospect of insurgent advances into important Alawite constituent communities for the regime in Latakia and the al-Ghab plain.
Blocking the possibility of these advances, and then inflicting a decisive defeat on the insurgency by retaking Aleppo city, served as the impetus for the Russian intervention in the fall of 2015. With those insurgent threats in the west now largely neutralized, the priorities have simply shifted. A lot of the discourse though failed to anticipate the eastward shift, believing that the regime and its allies did not have the manpower to retake the eastern areas and were only interested in "useful" Syria, rather than taking the regime's declarations on multiple occasions about retaking the whole country seriously.
In short, the Iranian land-route angle is being overplayed in the current events. But even supposing that such an ambition were driving the current offensive, one must ask whether the U.S. could actually stop this prospect from being realized. In the current circumstances, the Iranian forces and their allies would either have to take the Albukamal-al-Qa'im crossing between Deir az-Zor and Anbar, or construct a new route entirely. U.S. forces, meanwhile, would have to maintain an indefinite presence in the areas of Syria that could function as land-routes for Iran but are currently blocked off by the American presence.
Since before the Trump administration, U.S. policy had intended for Syrian rebel forces trained by the U.S. and Jordan from the remnants of the Deir az-Zor insurgency destroyed by the Islamic State to retake the eastern regions from the Islamic State. These forces initially came under the moniker of the New Syrian Army, which captured the Tanf border crossing with Iraq in the Syrian desert from the Islamic State in March 2016. Yet these rebels failed to make any meaningful advances beyond that, notably botching a raid on Albukamal. The rebels holding the Tanf border crossing have since been reconstituted as the Revolutionary Commandoes Army (RMA), but it is clear these forces and similar groups that were intended to retake Deir az-Zor province do not have the capability to do so.
Indeed, their spokesmen seem to exaggerate their numbers. A spokesman for RMA, one of whose commanders fled recently to regime-held areas, claimed his group has more than 1,000 fighters. It was further claimed that within a month, the group would have 4,000-5,000 fighters. A spokesman for the Qaryatayn Martyrs Brigade, a group that recently broke with the U.S. on account of a disagreement on fighting the regime's forces, similarly claimed to me that his group has 4,000 fighters. RMA, on the other hand, says that the Qaryatayn Martyrs Brigade only consists of approximately 300 fighters. Whatever the truth of these claimed figures, these groups are not sufficient in manpower to take Deir az-Zor province.
Thus, in the case of the Tanf border crossing, the American presence would be set to be stuck there indefinitely, likely subject to harassment by Iranian-backed forces falling short of all-out war. The only alternatives are either to try to pressure the Kurdish-dominated Syrian Democratic Forces (SDF) currently assaulting the Islamic State's de facto capital of Raqqa to launch a major offensive to take all of Deir az-Zor province (an unlikely prospect) and maintain a permanent U.S. presence and substantial economic commitment to SDF areas, or unilaterally deploy thousands of U.S. troops to take Deir az-Zor, only to face an insurgency that will either bolster the Islamic State or take on a different form. After all, the province was a source of fighters who ended up going to Iraq to fight the American presence there during the Iraq War.
In sum, the notion of confronting Iran in the east of Syria and blocking a supposed Iranian land-route may sound tough rhetorically but lacks a basis in reality. The idea of claiming a U.S. stake in the east of Syria and thus somehow being able to push for a political transition in the long run away from the Assad regime is fantasy. The Trump administration should resist calls to engage in a major escalation for a poorly defined objective that does not actually reverse what my colleague Kirk Sowell of Inside Iraqi Politics describes as "Iran's position as the pre-eminent player between Iran and the Mediterranean." Any U.S. policy-making should focus instead on dealing with the reality as it is and deterring threats that arise from it: that is, making clear that any actual attacks on U.S. assets and allies will be met with severe retaliation.