Reports have recently emerged that the US is in control of an airfield in Syria. The details are a bit sketchy and it’s hard to determine their veracity. For their part, US officials have either denied the allegations or refused to comment. But, if the reports are true, it would be important to understand if international law permits or prohibits such activities, as well as the ancillary problems that might arise. One notable issue is whether US control over the airfield puts the US at war with Syria.

To respect a country’s sovereignty, foreign countries that set up new airbases, or take control of old ones, most frequently do so with the consent of the host country on the basis of various terms and conditions. Absent consent, under international law the US would only be permitted to control the airfield — not to mention the airspace — by claiming an inherent right to self-defense or by acting under UN Security Council authorization. Otherwise, the US would infringe on Syria’s sovereignty in breach of international law.


The implication from the reports seems to be that the US didn’t obtain consent from the Assad regime. Instead, Al Jazeera reported that a “media activist” for the Syrian Democratic Forces (SDF) said, “[u]nder a deal with the YPG [an anti-Assad Syrian Kurdish group], the US was given control of the airport. The purpose of this deal is to back up the SDF, by providing weapons and an airbase for US warplanes.”

If that reporting is solid, a consent justification probably wouldn’t pan out. One possibility is that the US might have taken Syria’s silence on military action in the past as a form of consent now. Even so, a State Department spokesperson, when asked about US military action in Syria in the past was on record saying, “We’re not looking for the approval of the Syrian regime” (and Assad has since been less silent on the issue).

Alternatively, perhaps one could claim that the Assad regime no longer represents the sovereign State of Syria and instead the US relied on the YPG agreeing to the US presence on the airfield. But is the YPG the appropriate authority to grant consent? I highly doubt it. A non-State armed group — especially one that does not yet have a seat at the negotiating table for the future of Syria — is not conferred sovereign powers over an airfield (or the airspace the US would use to go to and from the airfield) — by virtue of controlling it. Perhaps the SDF sanctioned the YPG’s approval, but the US’s willingness to negotiate a peace deal with Assad makes taking such a position hard to untangle, especially from a political perspective. If others have insights into this issue, please do share them!

Sovereignty vs. Self-Defense

If the US doesn’t have consent to control the airfield, then a legal justification would have to be found elsewhere. Article 51 of the UN Charter reflects a State’s inherent right to individual and collective self-defense against an armed attack. There is also a widely held belief that under international customary law States have a right to self-defense prior to an attack having had occurred, but only when the “necessity of that self-defense is instant, overwhelming, and leaving no choice of means, and no moment of deliberation.” In other words, there must be an imminent threat of attack. That being the case, one could imagine the US claiming, as it has in the past, a right to individual self-defense due to the threats that ISIL poses to the US and/or the right to collective self-defense due to the threats that ISIL poses to Iraq and other countries in and out of the region.

But the story doesn’t end there. ISIL’s actions are not directly attributable to Syria. Also, the airfield is in what is internationally recognized as Syrian territory (i.e., the territory in question doesn’t “belong” to ISIL, or non-ISIL armed groups, under international law). Given US practice in the past, as part of a self-defense justification the US would likely specify that Syria is “unable or unwilling” to address the ISIL threat and the US therefore has the right to control the airfield — and use the necessary attendant airspace — as an offensive or defensive measure against ISIL attacks. If the news reports are accurate, my guess is that this is likely how the US is justifying its actions.

Be that as it may, it’s important to remember that self-defense claims are largely fact based and the Obama administration has whittled away at the notion of an “imminent threat” to the point that it “does not require the United States to have clear evidence that a specific attack on US persons or interests will take place in the immediate future.” Moreover, while a few States have referred to the “unable or unwilling” test in justifying operations against ISIL in Syria, I find it operationally problematic, especially when coupled with an expansive interpretation of “imminence.” Others point out that the test is not an established legal doctrine because States have not (yet) granted it a wide enough consensus. Finally, acts of self-defense must be regulated by necessity and proportionality, meaning that the US would have to show that control of the airfield was, in fact, necessary and proportionate.

UN Security Council Authorization

When the UN Security Council determines that a situation is a “threat to the peace, breach of the peace, or act of aggression,” it may authorize the use of force. For that reason, it’s worth considering, but ultimately dismissing, whether the US could rely on Security Council Res. 2249 to justify holding the airfield.

Res. 2249 condemns ISIL’s acts of terrorism as threats to peace and security and

[c]alls upon Member States that have the capacity to do so to take all measures, in compliance with international law, in particular with the United Nations Charter, as well as international human rights, refugee and humanitarian law, on the territory under the control of ISIL … in Syria and Iraq, to redouble and coordinate their efforts to prevent and suppress terrorist acts committed specifically by ISIL [and other groups] and to eradicate the safe haven they have established over significant parts of Iraq and Syria. (Emphasis added)

As others have pointed out, Res. 2249 is similar to previous resolutions that authorize coercive force but, critically, lacks the appropriate language and references. To take but one example, when the UNSC intends to authorize coercive measures it will usually invoke by name its power to do so under Chapter VII of the UN Charter. Res. 2249, however, makes no mention of such powers. Additionally, Res. 2249 actions must be taken in compliance with the UN Charter, which would logically mean the Resolution does not override the rules of territorial sovereignty, or Articles 2(4) and 51 for that matter. Thus, the US control over the base would still have to be justified by Syrian consent, a self-defense argument, or an appropriate UN Security Council Resolution.

Other Issues

Finally, it’s worth considering some of ancillary effects of the US’s control over the airfield, in particular whether Syria is entitled to retaliate with an armed response under jus ad bellum and, separately, if, under jus in bello, an international armed conflict now exists between the US and Syria where international humanitarian law applies.

If the US violated Syria’s territorial sovereignty by way of controlling an airfield, such a breach would likely not permit Syria to attack the US under the doctrine of self-defense, at least not yet. For that to happen, Syria would have to show that it was the object of an armed attack (as reflected in UN Charter Article 51) or it was threatened by an imminent armed attack (as defined under international customary law). However, based on the reported facts, the US’s control of the airfield doesn’t appear to have occurred by, or resulted in, an armed attack.

Alternatively, it could be argued that US control of the airfield constitutes a threat of force that’s in breach of UN Charter Article 2(4). But this too might be insufficient for Syria to make a self-defense claim, unless it can point to an imminent attack. (Note that this situation exposes the “gap” between Article 2(4) and Article 51, whereby a State can threaten the use of force, or even use force, in violation of Article 2(4) without it rising to the level of an armed or imminent attack.)

Separately, there is the question of whether US control of the airbase triggers the application of the 1949 Geneva Conventions and, thus the application of international humanitarian law. According to its Article 2(1), the Geneva Conventions apply when there is “armed conflict which may arise between two or more” States. That threshold alone may not be met by US control of the airfield, although it’s worth noting that the ICRC Commentary takes the view that “[a]ny difference arising between two States and leading to the intervention of members of the armed forces is an armed conflict within the meaning of Article 2” (emphasis added). It’s also important to consider whether the control of the airfield is part of a pre-existing international armed conflict where IHL already applies due to US airstrikes on Syria’s territory; an issue Dapo Akande has previously raised. If that’s the case, then it may be appropriate to analyze the taking of the airfield more through the lens of IHL than through the lens of the jus ad bellum.

One last point to consider: According to its Article 2(2), the Geneva Conventions also apply “to all cases of partial or total occupation of the territory … even if the said occupation meets with no armed resistance” (emphasis added). Under the definition of the 1907 Hague Regulations, occupation occurs when “[t]he authority of the legitimate power having in fact passed into the hands of the occupant.” This then raises the unique and novel question of whether the US could be defined as an occupying power, or as an emerging one, even if in only control of such a confined space as an airfield.

The ICRC’s Commentary envisaged Article 2(2) situations occurring only rarely and noted that “the number of persons protected may vary according to the course followed by military operations and the march of events.” The implication is that “the Convention automatically applies to” any protected person within that occupied territory. Moreover, and in keeping with the widely held interpretation that human rights law applies to those places where States have effective control, the US may incur human rights obligations that flow from the occupation of an airfield.

… But, then again, the specifics of this situation are only worth thinking about if the limited reporting on this issue is accurate. That said, President Obama’s October announcement that some 50 US troops would be sent to Syria raise many of the same issues outlined above.