Israel’s Use of Force Against Syria and the Right of Self-Defense

On December 8, the rebel group Hayat Tahrir al-Sham (HTS), augmented by other rebel forces, successfully overthrew the Syrian government of Bashar al-Assad following more than five decades of rule by his family. As Assad’s regime fell, the Israel Defense Forces (IDF) began a bombing campaign involving hundreds of air strikes in Syria against missiles, air defense systems, weapon production facilities that included those suspected of producing chemical weapons, and other military targets. Israel also destroyed the Syrian Navy in port. Israel has been periodically attacking Hezbollah, Iranian, and regime military assets for a period measured in years, but this time, it devastated Syria’s military capabilities. In explanation, Prime Minister Netanyahu announced that he had “approved the air force bombing of strategic military capabilities left by the Syrian military so that they will not fall into the hands of the jihadists.” 

Additionally, the day before Damascus fell, armed groups targeted UN Disengagement Observer Force (UNDOF) peacekeepers, temporarily taking control of several of their outposts. They were repelled with the help of the IDF. UNDOF was established to supervise the 1974 Agreement of Disengagement, which established a zone of separation between Israeli and Syrian forces following the 1973 Yom Kippur War. The following day, Prime Minister Netanyahu announced that he had ordered the IDF “to take over these positions to ensure that no hostile force embeds itself right next to the border of Israel.” He labeled the action “a temporary defensive position until a suitable arrangement is found.”

Some States have condemned the Israeli operations. For instance, Egyptian officials asserted they “violate international law, undermine the unity and integrity of Syrian territory and exploit the current instability to occupy more Syrian land.” But in a December 9 letter to the President of the Security Council, Israel’s UN Ambassador, placing the Council on notice of the IDF ground operations, stated, “The IDF will continue to act as necessary in order to protect the State of Israel and its citizens, in full accordance with international law.” But it also stated that “Israel is not intervening in the ongoing conflict between Syrian armed groups; our actions are solely focused on safeguarding our security.” According to the letter, Israel remains “committed to the framework of the 1974 Disengagement Agreement, including the principles regarding the Area of Separation.”

In this post, we examine whether there is any basis for the Israeli actions in international law, specifically the jus ad bellum. As we explain, the only potential justification for that use of force is self-defense under Article 51 of the UN Charter – even though the statements of Israeli officials to date have not mentioned the term, and Israel has not sent an Article 51 letter to the Security Council. However, as we will explain, even by an expansive approach to self-defense of the kind embraced in recent decades by US and UK governments, Israel’s actions cannot be justified as self-defense. 

We want to emphasize that our post is confined to examining the ad bellum legality of the operation. We will not be looking at questions of international humanitarian law (jus in bello), such as how the fall of the Assad regime affected the classification of any armed conflicts in Syria. It must also be emphasized that we are not taking on the more fraught issue of the Israeli actions’ policy and operational merit, or lack thereof. Reasonable minds may well disagree on that issue, regardless of what the law might say – but our sole focus will be on the law as it stands today.

Israel Has Used Force Against Syria

It is beyond dispute that bombing a State’s military assets qualifies as a “use of force” against that State, an action prohibited by Article 2(4) of the UN Charter and its customary international law counterpart. Similarly, it is indisputable that militarily taking control of another State’s territory is a use of force. Indeed, both actions are encompassed in the 1974 UN General Assembly’s Resolution 3314(XXIX), Definition of Aggression, which labels aggression “the most serious and dangerous form of the illegal use of force.”

Any of the following acts, regardless of a declaration of war, shall, subject to and in accordance with the provisions of article 2, qualify as an act of aggression:

(a) The invasion or attack by the armed forces of a State of the territory of another State, or any military occupation, however temporary, resulting from such invasion or attack…

(b) Bombardment by the armed forces of a State against the territory of another State or the use of any weapons by a State against the territory of another State;

…

(d) An attack by the armed forces of a State on the land, sea or air forces, or marine and air fleets of another State… (annex, art. 3).

Yet, this begs the question of whether the fall of the Assad regime, which controlled the assets that were attacked and the territory taken, affects the prohibition’s application. Its unanticipated overnight collapse and the disintegration of the armed forces complicate the determination of whether the HTS rebels, alone or with other armed groups, have formed an entity capable of representing Syria in its international relations. Under a traditional approach grounded in effectiveness, the rebels will qualify as the de facto government once they exercise effective control over the instruments of power in Damascus, as well as a majority of the State’s territory and population (1923 Tinoco Arbitration).

However, pinpointing the point of the new Syrian government’s establishment is immaterial for our purposes, for it is the State itself that is protected by Article 2(4)’s prohibition on the use of force. Accordingly, the fact that rebels overthrew Assad and may or may not have become the new government has no bearing on the status of the material targeted by Israel as State property or the territory the IDF moved into as that of the Syrian State. Israel has used force against the State of Syria, and that use of force would violate the UN Charter, absent an exception to the prohibition.

Self-Defense Against Future Attacks

The only exception to the prohibition on the use of force that Israel could conceivably rely upon would be self-defense. Article 51 of the Charter allows States to use force in self-defence in the face of an “armed attack.” Similarly, under the law of State responsibility, “The wrongfulness of an act of a State is precluded if the act constitutes a lawful measure of self-defence taken in conformity with the Charter of the United Nations” (ASR, art. 21).

Although Israel has not yet formally invoked its rights to defend itself forcibly under Article 51, statements by various Israeli officials can be read as doing so impliedly. A prime example is Prime Minister Netanyahu’s explanation that Israel is acting to prevent Syrian military assets from being used by “jihadists,” even though it remains unclear whether he is referring to the new Syrian government (HTS has jihadist roots) or other armed groups. It is also worth mentioning that a weakened Hezbollah, which has been very active in Syria, may be looking at the weapons and other military assets as fruit ripe for picking. Whether Hezbollah is doing so or not, it is certainly reasonable for Israel to harbor such concerns.

Similarly, in its notice to the Security Council, Israel justified the IDF’s move into the demilitarized zone established in the 1974 Disengagement Agreement on the basis of “protecting” Israel and “safeguarding” its security. Again, the implied justification is self-defense, in this case, against attacks mounted through that area.

Even before the current IDF operations, Israel repeatedly used force on Syrian territory without its consent. Most of the time, these limited strikes targeted assets tied to Hezbollah or Iran. Israel could at least make a colorable claim that it was acting in self-defense against ongoing or imminent armed attacks by these actors. Indeed, reports suggest that there may have been a line of communication between Israeli and Syrian authorities, through a mechanism mediated by Russia, regarding strikes targeting weapons transfers to Iranian-sponsored actors on Syrian territory.

Clearly, self-defense is the central legal issue in the current and past IDF operations. The question is whether Israel may plausibly rely on the right of self-defense to use force directly against the State of Syria by attacking its military assets on a considerable scale and moving into its territory to prevent a possible future armed attack against it by Syria, or by a non-State armed group operating from its territory, perhaps using the Syrian military assets.

It is widely accepted, although not universally so, that the right of self-defense extends to “anticipatory self-defense” in the face of an “imminent” armed attack (the terminology varies, often in a confusing manner). In other words, in the view of many States and scholars, States are not obliged to wait until the armed attack occurs before resorting to force to defend themselves. The question is how soon is too soon to act defensively.

One of the authors (Schmitt) has long taken a permissive approach to matter. Over two decades ago, he asserted,

[I]t would be absurd to suggest that international law requires a State to “take the first hit” when it could effectively defend itself by acting preemptively. This being so, the correct standard for evaluating a preemptive operation must be whether or not it occurred during the last possible window of opportunity in the face of an attack that was almost certainly going to occur. Restated, it is appropriate and legal to employ force preemptively when the potential victim must immediately act to defend itself in a meaningful way and the potential aggressor has irrevocably committed itself to attack.

A use of force that does not comply with this “last window of opportunity” approach, in his view, is merely “preventive” and, therefore, unlawful. This might be because there were alternative means of addressing the situation or because of a lack of certainty as to whether the armed attack will be mounted. The approach was later adopted by some States, including the United States (see, e.g., here). It reflects the condition of “necessity” when acting in self-defense, one that, together with proportionality, is universally accepted (see, e.g., Paramilitary Activities, paras. 194, 237; Nuclear Weapons, para. 41; Oil Platforms, paras. 43, 73-74, 76).

The other author (Milanovic) has not been as comfortable with what he sees as normative entrepreneurship by some Western governments in pushing the envelope of anticipatory self-defense. In particular, he has written about two different approaches to defining an “imminent” armed attack (see here and here). One is more restrictive and temporal in character (i.e., an imminent armed attack is one that is about to occur). The other is more permissive and of causal character (i.e., an imminent armed attack will occur, absent outside intervention in the causal chain, because the attacker has committed to it). The latter is, of course, subject to greater possibility of abuse. The causal approach, albeit with a substantial degree of conceptual fudging, is evident in the so-called Bethlehem Principles that some States have endorsed (see also Akande and Lieflander here).

Both of us agree, however, that even the most permissive reasonable conceptions of self-defense in response to future attacks require such attacks to be imminent in the causal sense given above. In other words, if the Israeli actions do not satisfy the last window of opportunity test, they would also not fulfill the more restrictive interpretations of the necessity criterion; they would be unlawful.

For that test to be satisfied, there would need to be evidence either that the new government of Syria had irrevocably committed itself to attack Israel in the future or (more controversially) that armed groups operating in Syria harboring the same intent would obtain access to weapons of the Syrian military and/or attack through the territory into which the IDF has now moved. If such evidence existed, further questions of necessity and proportionality would arise – essentially, would a use of force by Israel today be the only available means to stop this inevitable future attack, and was the scale of the Israeli anticipatory defensive response limited to that necessary to prevent it?

From what is publicly known today, it is difficult to conclude that there is an imminent armed attack against Israel, either by Syria or by armed groups operating within Syria that would use Syrian government assets. Of course, most of the groups are hostile to Israel; indeed, some are fairly characterized as “jihadists” or terrorists (see, e.g., the US terrorist list). As noted by President Biden, “Make no mistake, some of the rebel groups that took down Assad have their own grim record of terrorism and human rights abuses.” In our opinion, it is not unreasonable for Israel to conclude that some of the rebel groups are a threat, that the military assets it destroyed might one day be used in attacks against Israel, and that such attacks could be mounted through the Golan Heights and the adjacent area.

But from those threats alone, we cannot infer an irrevocable commitment – a decision that will be implemented – to attack Israel. Even Israel’s closest ally, the United States, has taken a wait-and-see approach. As President Biden observed, “We’ve taken note of statements by the leaders of these rebel groups in recent days and they’re saying the right things now. But as they take on greater responsibility, we will assess not just their words but their actions.”

Not only have the new Syrian leaders not expressed an intention to attack Israel, but they seem occupied with trying to consolidate power in a devastated State. It is, accordingly, difficult to treat Israel’s use of force as necessary in the sense that now represents the last window of opportunity to deflect a future attack. The current disarray in the Syrian armed forces allowed Israel to easily and quickly strike some of its objectives and move into the demilitarized zone. Still, the situation is not one where waiting would necessarily mean forfeiting the opportunity to act at a later date. We are not convinced that Israel needed to act at the present time because the window of opportunity to defend itself against a future armed attack by Syria, using Syrian weapons, or from Syria was about to close.

Finally, we note that some have taken the position that once a State is acting in self-defense in a “comprehensive” manner, the necessity and proportionality criteria no longer need to be applied as the armed conflict continues (Dinstein, War, Aggression and Self-Defence, pages 281-287). They would point to the comprehensive nature of the Yom Kippur War and the fact that there have been exchanges between Syria and Israel since then despite the Disengagement Agreement. Although we admit that States sometimes act in this manner, the approach does not, in our estimation, reflect international law.

Concluding Thoughts

The disarray in Syria undoubtedly presents security risks to Israel. It is possible the new regime might turn its sights towards Israel. It is equally possible that some of the Syrian military weapons might be seized by armed groups and used at some later date against Israel. And it is possible that attacks could be mounted through the territory into which the IDF has moved. No one could reasonably deny the existence of these risks. In light of them, reasonable policy-makers and military experts might conclude that some of those risks – in particular, the one stemming from chemical weapons – are unacceptable, no matter what the law says.

However, our purpose has not been to assess the practical wisdom of the Israeli actions, but rather their compliance with the jus ad bellum. The law is clear on this point – security risks or threats do not themselves give rise to the right to self-defense. Only ongoing or imminent armed attacks do. In our view, a purely preventative theory of self-defense, one that is solely about mitigating (often subjectively perceived) security risks, would put the use of force prohibition on a dangerous slippery slope.

Such a theory is sometimes, correctly or not, associated with the George W. Bush administration’s 2002 National Security Strategy. Yet, it is not the current administration’s approach nor that of the United States’ closest ally, the United Kingdom. As that State’s Attorney General observed in formal legal advice regarding the 2003 invasion of Iraq,

there must be some degree of imminence. I am aware that the USA has been arguing for recognition of a broad doctrine of a right to use force to pre-empt danger in the future. If this means more than a right to respond proportionately to an imminent attack (and I understand that the doctrine is intended to carry that connotation), this is not a doctrine which, in my opinion, exists or is recognised in international law.

We agree. While States have the right to defend themselves anticipatorily against armed attacks, they do not have the right to use force against other States simply because they perceive them to be security risks or threats, whether these perceptions are objectively valid or not. They also have no right to demilitarize their neighbors who have not attacked them, including by destroying their air defenses or navy. Thus, whatever the policy calculus might be from an Israeli perspective, we do not see how Israel’s use of force against Syria could be justified from an ad bellum standpoint, as the law stands today.