Turkey’s latest military offensive in northern Syria has triggered a heated discussion about the legality of the use of force. While operation ‘Peace Spring’ has been dubbed ‘unlawful’ by most commentators, the community of states has so far focused its criticism on the military, security, and humanitarian dimensions of the invasion. The reluctance of governments to offer their views on its legality is unfortunate, given that such views (opinio juris) are crucial to the evolution of customary international law on the use of force.

Germany, which is traditionally skeptical of the use of military force abroad, has raised some tentative concerns over the legality of the operation. Those concerns have recently been elaborated and substantiated by Germany’s Parliamentary Research Service.

Similar to the U.S. Congressional Research Service, the Wissenschaftliche Dienste functions as the research arm of Germany’s federal legislative chamber, providing background information, policy briefings, and extensive legal expertise to its members, regardless of their party affiliation. As a parliamentary branch agency, its official mandate is purely consultation. That said, its analysis and positions are widely respected among German policymakers and have often figured prominently into the country’s public discourse.

The short report produced by the Parliamentary Research Service on the Turkish invasion of northern Syria offers a comprehensive but also highly critical discussion of various legal aspects of Turkey’s military operation. Its conclusion is clear: operation ‘Peace Spring’ is unlawful and could have potential legal consequences for President Recep Tayyip Erdoğan.

This article will briefly summarize the report’s key points.

Claim of Self-Defense Is Unconvincing

At the heart of the report lies a detailed legal analysis of Turkey’s letter sent to the U.N. Security Council on Oct. 9, in which Ankara invoked the right to self-defense:

Turkey initiated Operation Peace Spring on 9 October 2019, in line with the right of self-defence as outlined in Article 51 of the Charter of the United Nations, to counter the imminent terrorist threat, to ensure Turkey’s border security, to neutralize terrorists starting from along the border regions adjacent to Turkish territory and to liberate Syrians from the tyranny of PKK’s Syrian branch, PKK/PYD/YPG, as well as Deash. Turkey’s national security has been under the direct and imminent threat of terrorist organizations operating in the east of the Euphrates in Syria, among which Deash and PKK/PYD/YPG are at the forefront. The PKK/PYD/YPG terrorist organization has continued to find breeding ground in the north-east of Syria and has become a serious threat for regional and international security, as well as for the territorial integrity of Syria. In particular, PKK/PYD/YPG units close to Turkish borders in the north-east of Syria, continue to be a source of direct and imminent threat as they opened harassment fire on Turkish border posts, by also using snipers and advanced weaponry such as anti-tank guided missiles…

Two key issues here are the invocation of Article 51 to justify military force against a non-state actor and the existence of an armed attack or imminent threat of armed attack (or lack thereof) at the time of Turkey’s operation. On the first, international lawyers have debated for quite some time whether non-state actors can mount an armed attack that would allow a state to invoke the right of self-defense under Article 51. In at least three separate decisions, the International Court of Justice (ICJ) made clear that the attack must be attributable to a state for the exercise of self-defense on that state’s territory to be lawful. The ICJ’s restrictive reading of self-defense, however, has been challenged more recently with suggestions that the need to attribute an armed attack by non-state actors to a state is no longer a necessary condition for the right to use force in self-defense. For example, according to Kimberley Trapp, professor of Public International Law at University College London, ‘the Court’s decisions do not preclude uses of defensive force against (and only against) NSAs in foreign territory.’

While the German research service’s report does not offer a definitive position on the issue, it does suggest that a right to self-defense against non-state actors exists when those actors exercise some kind of ‘territorially manifested authority,’ as in the case of the Kurdish YPG-Militia.

The second problem, however, is that in order to invoke Article 51, Turkey would have to provide sufficient evidence to substantiate the claim of an armed attack. This would include demonstrating that an armed attack was underway, or at least imminent, at the time of Turkey’s operation. According to the Parliamentary Research Service, none of those threshold criteria were met. Interestingly, the report suggests that in order to prevent the abuse of Article 51, the evidentiary threshold for a state to claim the right to self-defense against non-state actors is higher than for ‘traditional’ interstate conflicts.

The authors of the report also point out that the term ‘armed attack’ that would trigger self-defense under Article 51 is nowhere to be found in Turkey’s letter of justification. There has been some discussion within the international legal community whether a series of attacks can, taken together, provide the basis for invoking the right of self-defense (accumulation of events doctrine). According to the report, however, such a doctrine has not evolved into customary international law (yet); and the letter seems to suggest that Turkey is not trying to advance such a claim.

Last, the report notes the absence of any reference to the (legally controversial) ‘unable or unwilling’ doctrine, which would allow Ankara to argue that Syria is neither able nor willing to prevent Kurdish militia from launching attacks on Turkish territory.

The report does not address the issue of whether Turkey is already in an armed conflict with the YPG by virtue of the fact that it sees the PKK-YPG as one and the same.

In conclusion, the German Parliamentary Research Service finds that even under a broad reading of the right to self-defense, Turkey cannot invoke Article 51 in order to justify its military offensive in Syria.

Misreading the Adana-Agreement

In addition to invoking the right to self-defense, Turkey’s letter refers to the so called Adana-Agreement in order to justify its military offensive:

Besides, the Adana agreement signed on 20 October 1998 by the Republic of Turkey and the Syrian Arab Republic constitutes a contractual basis for my country to fight all kinds of terrorism emanating from Syrian territory in its hideouts and in an effective and timely manner.

The agreement between Turkey and the Arab Republic of Syria was signed in 1998 and regulates their cooperation in the fight against terrorism. The treaty was originally established against the backdrop of Turkey’s long-standing fight against the PKK and obligates the two countries to coordinate their anti-terrorism activities through the exchange of special advisors and high-ranking military officials.

Nothing in the agreement, however, suggests that the two signatories agree to territorial secession, a ”safety-zone” or an occupation on the other state’s territory. As the report notes, “the treaty does not constitute the right to a unilateral invasion.” This view seems to have been confirmed by Turkey’s former intelligence chief, İsmail Hakkı Pekin, who noted that the agreement does not allow Ankara to conduct military offenses on foreign territory.

Military Occupation, Resettlement, and the Crime of Aggression

Given the absence of a convincing claim to self-defense, Turkey’s establishment of a safety zone in Northern Syria is clearly unlawful. Even in the hypothetical case that a right to self-defense could be invoked, the report notes, such a measure would be disproportionate. While acts of self-defense can include military activities on foreign territory, Turkey’s safety zone bears a strong resemblance to what the authors of the report call an “ethnic-corridor cleaning;” that is, Turkey’s actions will, in practice, force civilian populations in and out of certain areas within the Kurdish parts of northern Syria. Here, the report points to the law of military occupation and Article 49 of the 1949 Geneva Convention, which prohibits any resettlement of protected people within occupied territories. The issue has been usefully discussed here.

If one accepts the report’s legal analysis, then Turkey’s latest military offensive in Syria constitutes a clear violation of the prohibition of the use of force outlined in Article 2(4) of the U.N. Charter. Given that the International Criminal Court has recently extended its jurisdiction to the crime of aggression, the German Parliamentary Research Service argues, President Erdoğan could be held criminally responsible for the invasion. Though some legal commentators have sketched out such a scenario, an investigation by the ICC seems highly unlikely – the U.N. Security Council would need to refer the case to the Court, and it seems none of the permanent members is particularly keen on such a scenario.

NATO and Collective Self-Defense

Finally, the report considers the potential involvement of NATO. Some German politicians and journalists have raised concerns that Turkey’s NATO partners could be dragged into the conflict, even as German Defense Minister Annegret Kramp-Karrenbauer has suggested further German involvement. From a legal perspective, the report states, worries about increased NATO exposure are unfounded. Article 5 of the NATO treaty, which regulates the alliance’s collective self-defense mechanism, does not stipulate an “automatic trigger”; any act of collective self-defense has to be decided by consensus.

Moreover, Article 5 explicitly refers to an “attack” against an alliance partner, thereby calling for a strict distinction between an act of aggression and an act of self-defense. Should Turkey consult the NATO Council and insist on its right to trigger Article 5 and collective self-defense, the report concludes, questions could be raised over the potential abuse of the alliance’s collective defense mechanism, i.e. Ankara essentially provoking an armed attack only to then claim collective self-defence under Article 5.

Overall, the report is clear and candid, leaving no doubt that Turkey’s latest Syria invasion is unlawful. While this is of little help to those who have been suffering the humanitarian consequences of Ankara’s decision, it does offer a crucial counterbalance to some of the reckless post-9/11 interpretations of Article 51 put forward by Turkey and others. It also serves as an important reminder that evidence and proportionality matter, and that exceptions to the prohibition of the use of force should remain tightly defined rather than broadly construed.

IMAGE: A woman walks by a crater caused by a car bomb explosion in the town of Suluk in Syria’s Turkish-controlled Tal Abyad border region on Nov. 10, 2019. Turkish authorities said at least eight people were killed and more than 20 wounded. (Photo by ZEIN AL RIFAI/AFP via Getty Images)