Regulating Military Force Series – Enduringly Unwilling and Unable: The Syrian Chapter of the Forever Wars Saga

Editors’ note: The author delivered remarks on the subject of this post at the conference “International Law and the Regulation of Resort to Force: Exhaustion, Destruction, Rebirth?” at the Centre for International Humanitarian and Operational Law, Palacký University in Olomouc, Czech Republic.

While largely faded from the public consciousness, the last page has not been turned in the Syrian chapter of the United States’ “forever wars” saga. Since 2014, U.S. troops have been targeting Al Qaeda and the Islamic State of Iraq and Syria (ISIS) within Syrian territory, against the will of the Syrian government, as a part of a broader counterterrorism campaign.

As of November 2023, about 900 U.S. troops still remain in Syria. Airstrikes have supported this effort, but have also been used to target other actors, such as the Syrian government, Iran’s Islamic Revolutionary Guard Corps, and its affiliated militias. Both the initial intervention against ISIS, and subsequent strikes against Iranian-backed militias, have been justified under self-defense and the “unwilling or unable” doctrine. In this post, I examine the temporal limitations of the “unwilling or unable” doctrine, specifically whether the justification loses its force when territorial state itself becomes willing and able.

The American Interpretation

The United States’ understanding of the “unwilling or unable” doctrine is spelled out in the 2016 report Legal and Policy Frameworks Guiding the United States’ Use of Military Force and Related National Security Operations (the Frameworks Report). It explains that States may defend themselves from actual or imminent armed attacks by a non-State armed group in the territory of another sovereign State without its consent, where the territorial State is unable or unwilling to prevent the use of its territory by the non-State actor for such attacks.

The Frameworks Report goes on to stress that this standard is “not a license to wage war globally.” Instead, it is meant to ensure that the sovereignty of other States is respected, as it only authorizes the use of force in those exceptional circumstances where a State will not or cannot suppress a threat that is emanating from its territory. Despite its exceptionality, no specific carve-out is provided in the report from the general provision that the legality of the use of force in self-defense need not be continuously reassessed during hostilities. As a result, the Frameworks Report permits the reading that a State invoking the “unable or unwilling” doctrine is justified in continuing an intervention in another sovereign territory against its will, even if the territorial State regains the ability and willingness to address the threat.

This reading of the customary law would mean that the United States is justified in remaining in Syria until it has concluded all hostilities with ISIS, Al Qaeda, and its offshoots worldwide, regardless of the Syrian government’s ability and willingness to address these groups’ activities or the level of threat emanating from its territory. Given that the current U.S. engagement in counter-terrorism operations against these particular actors has been going on for over two decades and spans the globe, this understanding of the law would give the justification a seemingly endless endurance. This reading therefore seems to strike a different balance between the right of self-defense and respect for State sovereignty than that envisaged in the overall legal framework.

It is also at odds with the operation of the overarching legal framework and analogous international legal norms, as well as State practice in this area. In a forthcoming book chapter, I analyze the substance and temporal limits of the doctrine in detail through all three of these lenses and find that most arrows point in the direction of mooting the justification if a State regains the ability and willingness to address the threat. In this post, I focus on the State practice of States that have invoked the doctrine.

The Substantive Indeterminacy of the Unwilling and Unable Doctrine

First, it should be noted that the doctrine itself is highly contentious, and it is unclear that it has actually ripened into customary international law. At last count, about thirteen States recognize it as custom, while States like Brazil and Mexico fiercely oppose it, and most other States have remained silent on the issue. There is also some scholarly support for such a customary norm, but most scholars remain skeptical, especially in light of the 2021 UN Security Council Arria-Formula Meeting, where it became clear that “no common view” on the doctrine had been reached and “substantive differences remain[ed].”

Even if some version of the doctrine has made its way to customary law, there is no agreed substance or temporal limitation of such a doctrine, and States are generally reluctant to flesh out the details when invoking it as a justification. The substantive indeterminacy of the doctrine makes it ripe for abuse at best. At worst, it threatens to wholly undermine the non-intervention principle enshrined in the UN Charter. Notwithstanding these risks, States invoking this justification have largely been consistent in their overall practice so far, indicating which doctrine they are relying on, which non-State actor the intervention is targeting, and ending the intervention when the territorial State is deemed willing and able.

State Practice on Temporal Limits

The “unwilling or unable” doctrine was first invoked in what seems to be the origin story of all customary use of force norms, the Caroline incident. In total, the record shows that a version of this justification has been invoked against non-State actors a total of nine times (see Appendix 1). This includes: the United Kingdom in the United States in 1837; Israel in Lebanon in 1978-84; Israel against Lebanon and Syria in 1996; Turkey in Iraq in 1995-97; the United States in Afghanistan and Sudan in 1998; the United States in Afghanistan in 2001; Russia in Georgia in 2002; Israel in Lebanon in 2006; and the United States in Pakistan in 2011.

Excluding the interventions carried out by the United States, six cases remain. Of these six cases, five support the position that an intervention should end when the territorial State has regained the ability and willingness to suppress the threat, rather than at the end of hostilities, while the remaining case provides support for neither position. Looking at the interventions in chronological order, this support has also remained stable over more than 150 years.

In the now famous Caroline incident, British forces torched an American steamer that the rebels were using to transport themselves from the U.S. side of the Niagara River to the Canadian side. But they quickly withdrew once the United States had regained ability and willingness. While there was disagreement between the parties over whether the United States was in fact “unwilling or unable,” both parties agreed that this justification at least did not endure after December 16, 1837, the day of the elimination of the immediate threat posed by the steamer ship. Although individuals on American territory continued to support the rebellion following the incident, the British left enforcement measures to “the protective intervention of any American authority.”

The UN Security Council’s (UNSC) reaction to the 1978 Israeli intervention into Lebanon, dubbed “Operation Litani,” targeting members of the Palestinian Liberation Organization (PLO) and other Palestinian groups also placed the onus on Lebanon’s regained ability and willingness. Five days after the start of the invasion, the UNSC adopted Resolution 425 calling for an immediate withdrawal of Israeli forces from Lebanon. In addition, Resolutions 425 and 426 called for the establishment of an interim UN force (UNIFIL) that would confirm Israeli withdrawal and ensure the return of effective Lebanese control over the area.

While not explicitly stating whether Lebanon was sufficiently able and willing to suppress the threat to Israel posed by the Palestinian groups, the UNSC implied through these resolutions that such a status would at least be attainable in the short term with the support of the interim force, and that the continued presence of Israeli forces therefore was not justified.

Almost two decades later, the international community once again put pressure on Israel to disengage from a high-intensity campaign launched in Lebanon, this time targeting Hezbollah. The 1996 Israeli “Operation Grapes of Wrath” was meant to “pressur[e] the Syrian and Lebanese governments to fight concretely against the actions of Hezbollah.” Amidst a backdrop of escalating cycles of violence and mounting civilian casualties, the UNSC passed Resolution 1052 calling for a ceasefire and expressing support for the ongoing mediation effort led by the United States. On April 26, the parties signed the “April Understanding,” which obligated the governments of Israel and Lebanon to ensure that armed groups in Lebanon did not carry out any attacks into Israel and to refrain from targeting civilians or allowing civilian areas to be used to launch attacks.

Here, there seem to have been dual drivers behind the Israeli disengagement. First, there was a considerable amount of international pressure. Second, Lebanon and Syria agreed to renew their commitment to suppress Hezbollah attacks against Israel. However, the commitment was a weak one as it did not require Lebanon to dismantle Hezbollah like Israel had been pushing for. At the same time, it is clear that the Israeli disengagement was not a result of the end of hostilities exactly because there was no dismantling, defeat, or even significant degradation of Hezbollah. In conclusion, it therefore seems that Israeli disengagement in this case was primarily based on international pressure and negotiation efforts rather than Lebanon’s ability and willingness or the end of hostilities, and therefore this example does not provide significant support for either position.

The Turkish intervention into Iraq targeting the Kurdistan Worker´s Party (PKK) that started in 1995 and continued sporadically until 1997 is also somewhat of a mixed bag. While the first withdrawal after the initial intervention dubbed “Operation Steel” took place after the Kurdistan Democratic Party´s delegation to Turkey promised that the Kurdistan Regional Government would suppress the threat posed by PKK in Iraqi Kurdistan, the later explanations for withdrawals were consistently vague, simply nodding to “mission success” (Roger Chapman, A History of Counterinsurgency vol.2, p. 328).

The last withdrawal in 1997 coincided with a ceasefire that largely held until a formal peace treaty was put in place. Without a clearly stated reason from the Turkish government, this last withdrawal therefore could be interpreted as lending support to either of the two positions. Because it coincided with the end of hostilities, this might be the reason for withdrawal.

On the other hand, because the end of the civil war would also further enable a Kurdish Regional Government to suppress the threat posed by the PKK, the withdrawal may also have been motivated by the regained ability and willingness of the territorial State. The details of the peace agreement signed by the two warring factions bolster the latter view, as it contained a pledge to deny use of northern Iraq to the anti-Turkish PKK.  In conclusion, this case as a whole lends more support for the position that an intervention should end when the territorial state has regained an ability and willingness to suppress the threat.

The 2002 Russian intervention in Georgia’s Pankisi Gorge targeted separatist Chechen rebels. In addition to demanding that Georgia step up its efforts to suppress the threat, Russia launched airstrikes and started preparation for a more substantive intervention. This was met with swift reactions from the Georgian government, and the United States, which was involved in a “train and equip” effort in Georgia. That effort, perhaps in combination with international pressure, was enough to push the parties into a border cooperation agreement.

While that outside pressure might have muddied the water a little for the evidentiary value of this case, there is no doubt that all parties involved focused on Georgia´s willingness and ability throughout the incident, rather than the defeat of the Chechen rebels, indicating that this was the central focus for withdrawal. Indeed, Russia had even spelled out in its letter to the UN Secretary General that “none of this will be necessary, no measures or special operations will be needed if the Georgian leadership actually controls its own territory.” Similarly, Georgia focused on its willingness and ability to stamp out the threat, stating that “[i]n line with its obligations under resolution 1373, Georgia had completed anti-terrorist and anti-criminal operations in the Pankisi Gorge” and that “[f]ull control over the territory had been reestablished and there were no longer any Chechen fighters, terrorist suspects or mercenaries in the Gorge.”

The 2006 Israeli intervention in Lebanon, often referred to as the July War, targeted Hezbollah and lasted for 34 days. On August 11, the UNSC unanimously adopted Resolution 1701 calling for an immediate ceasefire. Driving the resolution was, among other things, a “commitment of the Government of Lebanon, in its seven-point plan, to extend its authority over its territory, through its own legitimate armed forces, such that there will be no weapons without the consent of the Government of Lebanon and no authority other than that of the Government of Lebanon.” The Israeli Ambassador, Dan Gillerman, also made clear that the only way to avoid further tension between Israel and Lebanon was by Lebanon “disarming and disbanding Hizbollah and other militias, as well as by Lebanon’s exercise of authority over all its territory.”

The statements by the Israeli ambassador here, as well as inclusion of the language about Lebanon´s commitment and ability to suppress the threat in the UNSC Resolution, lends support to the position that an intervention should end when the territorial State has regained an ability and willingness to suppress the threat.

Striking the Right Balance

With five out of six cases supporting a temporal limitation of this justification based on the territorial State’s regained ability and willingness, these examples provide a striking majority of practice for States to lean on when formulating their position on this matter. It should of course be noted that six cases, involving only a handful of States and without opinio juris attached, hardly provides a basis for the crystallization of customary international law. On the other hand, even less support is provided for a justification that endures to the end of hostilities, regardless of the territorial State’s ability and willingness. In this case, the practice also points towards the arguably most ideal operation of the doctrine, providing a sensible balance between the victim State´s security and the territorial State´s sovereignty, similar to the largely analogous rights of belligerent parties under neutrality law.

Even if States that invoke this doctrine do not yet accept this temporal safeguard as customary international law, they should at a minimum adopt it as policy. This is especially true for the United States in Syria. While there may have been convincing moral and policy arguments (and even legal arguments in light of UNSC Resolution 2249) for intervening against ISIS to protect civilians in 2014, the current vague objective of securing the “enduring defeat” of ISIS do not justify maintaining a military presence in Syria in 2024. The seemingly endless reliance on the “unable or unwilling” doctrine to use force in Syria (including against actors other than ISIS), and even occupy territory against the will of the Syrian government does not only find shaky support under international law, but also threatens to erode the rule of law in the region and elsewhere, and the United States’ reputation for respecting international law.

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Photo credit: Spc. Jensen Guillory