Preemption or Reprisal? Analyzing President Biden’s Airstrike in Syria

With his recent airstrike in Syria, President Biden fell in line with a corrosive interpretation of both jus ad bellum and international humanitarian law (IHL) that has been employed to justify various U.S. military activities in the Middle East for twenty years. On February 25, 2021, the President approved an airstrike on the Iranian-Syrian border. The strikes were made in response to a rocket attack on February 12, 2021 by Iranian militants against American coalition personnel in Iraq. While that attack was not committed by Iran, the militia responsible were reportedly backed by the Iranian government.

With this strike, Biden indicated his administration has no intention of deviating from a dangerous IHL interpretation that is both incongruent with actual doctrine and undermines the integrity of the right to self-defense. This recurring justification, which is largely a progeny of the War on Terror, has two key elements: first, the blurring of jus ad bellum and jus in bello frameworks; and second, using this muddled interpretation to justify the use of reprisals under the guise of self-defense. These two practices have placed the executive branch on a path-dependent approach to U.S. military activity in the Middle East, which is reshaping IHL in a destructive way. 

Jus ad Bellum and Jus in Bello: A Blurred Line

Turning to the first element, the administration’s justification for this strike relies on inaccurate IHL language. The Pentagon claimed the strike was “in response” to the recent militia attacks against American interests in Iraq and the “ongoing threat to those personnel.” In a letter to Congress, President Biden claimed the strike was “pursuant to the United States’ inherent right of self-defense as reflected in Article 51 of the United Nations Charter.” Finally, in a statement to reporters, Press Secretary Jen Psaki said:

“The targets were chosen to correspond to the recent attacks on facilities and to deter the risk of additional attacks over the coming weeks…The strikes were both necessary to address the threat and proportionate to the prior attacks.”

Examining these justifications under the jus ad bellum and jus in bello frameworks, note that Secretary Psaki’s statement makes explicit references to use of force buzzwords including the principles of necessity and proportionality. It further claims the selected targets “correspond” to the previous attack by Iranian militia, and that the aim was to “deter the risk” of future attacks. However, the argument does not align with IHL’s standards for the legal use of force. The reason—in an oversimplified explanation—is that the U.S. is suspended in a type of conflict that does not align with the very understanding of armed conflict in IHL.

For the use of force in self-defense to be lawful, it must comply with both the jus ad bellum and jus in bello frameworks under international law. Regarding the former, a state must have just cause in resorting to the use of force. In the post-UN Charter world, just cause exists in three circumstances: where the target country has consented to force being used on its territory, where the UN Security Council has authorized force under Chapter VII, and where a state is exercising its right to self-defense. Further, Article 2(4) of the UN Charter, and its subsequent interpretation, prohibits the use of reprisals. Therefore, as no consent nor Security Counsel authorisation is applicable here, the only justification on which the US may rely for its strike is the right to self-defense. The UN Charter recognizes this customary right of states in Article 51.

As to the latter, jus in bello dictates what means of force may be lawfully used during an armed conflict. This includes limitations on who may and may not be targeted, what weapons may and may not be used, and the justifications required for each individual military act. What elements of these legal frameworks are implicated depends on the nature of the ongoing conflict—provided that there is one.

Psaki’s statement attempts to couch the strike in applicable jus ad bellum language, but in doing so reveals the U.S government’s ongoing confusion—or indifference—in reserving these attacks for when the self-defense justification actually applies. The immediate consequences are threefold. First, the Biden administration’s position confuses what factors the proportionality principle considers. Proportionality in the context of self-defense does not mean weighing the harm suffered by the initial attack and the responding attack in some Utilitarian terms. Rather, proportionality refers to the exact amount of force required to repel an armed attack, without causing any additional harm. Thus, proportionality is impossible to weigh adequately without its twin element of necessity, which is the second component this argument lacks.

Viewing the use of force, as international law does, as a last resort, the U.S. fails the necessity principle by its own admission.  “Deterring the risk” of possible future attacks does not constitute “necessity” for the use of force. Necessity in self-defense dictates that the use of force must be the only option to repel a threat, which is informed by the threat’s imminence—i.e. “instant, overwhelming, and leaving no choice of means, and no moment for deliberation” (Caroline Affair). Where oncoming danger is not imminent, as no “risk” alluded to here was, that danger does not demand force to be repelled, and so necessity is simply not present.

Third, the administration’s statement seems to imply it viewed the conflict with Iran as ongoing—which is an amorphous gray-zone the War on Terror continuously expands. However, the choice of target implicates jus in bello issues, as the target of the strike was also unlawful. Jus in bello’s requirements for who and what may be targeted in an ongoing conflict were shirked here, where the U.S. decided to conduct an armed attack in Syria, instead of Iran—the state responsible for the previous attack—or Iraq—the state in which the previous attack occurred. This is further complicated by a lack of clarity as to whether the facilities targeted in the strike were in fact those used by the militia responsible for the 12 February attack. The Secretary of Defense only said he was “confident” that the structures targeted were used by the same militias. However, even if Defense Secretary Lloyd Austin is correct and these facilities truly were connected to the militia responsible, it does not excuse conducting an attack on Syrian territory.

The Biden administration justified this as a strategic choice: to avoid causing problems for the “fragile U.S.-allied” Iraqi government. But that choice was not an option under the laws of war. Furthermore, when the U.S. decided to escalate this ongoing conflict by incorporating the territory of another sovereign state, the jus ad bellum inquiry is triggered again—and in that inquiry, the U.S.’ argument is likewise defeated. For an attack in Syria to have been appropriate under Article 51 self-defense, the attack by the militia would need to be imputable to the Syrian government—or at least, made possible by their willful ignorance of the militia’s actions—and then would further need to meet the requirements of immediacy, necessity, and proportionality. As this attack did not emanate from Syria or Syrian territory, Article 51 is not available as a justification for targeting militia facilities on Syrian soil.

A Reprisal by Any Other Name

Turning to the second element, the Biden administration’s justification does a poor job at disguising that the airstrike was, in fact, purely a reprisal. The threat to which Biden’s strike “responded” had occurred ten days prior. The attack was not ongoing, nor—per any available information from the U.S. Government—was there an imminent threat to repel. Yet the clearest indicator that this strike was retaliatory, and not a product of genuine self-defense, is in comments made by Biden’s administration, and even the President himself. Psaki claims earlier in her statement that the President has a “right to take action…in a manner of his choosing,” which is patently false. The President has a right to repel imminent or ongoing armed attacks, and many have argued, this is simply not present here. Biden’s own comment on his rationale behind the attack acknowledges this, saying: “You can’t act with impunity. Be careful.” This strike was not defensive, it was retaliatory, plain and simple.

While we can rightly criticize the Biden administration for muddling IHL doctrines to justify armed reprisals, we also can’t ignore that this practice has built up two decades of momentum, and resisting this current is a daunting task. In becoming president, Biden inherited the legal and practical challenges of the War on Terror. In this context, America has a weighty tradition of engaging in legal gymnastics, working to make the self-defense doctrine concur with the United States’ desired foreign policy in the region.

This can be seen in the Bush Administration’s novel National Security Strategy introduced in 2002, which asserted the right of “preemptive” or “anticipatory” self-defense. The Bush Administration argued that, as modern adversaries rely on military tactics that make prospective attacks nearly impossible to anticipate, “a more flexible standard for determining necessity” is appropriate. While this argument was used to justify the U.S. invasion of Iraq, it has been reupholstered repeatedly to serve as justification for one remote strike after another—continuing to muddy the distinction between the justification for going to war and justifying specific acts during a conflict.

Biden’s recent airstrike has reaffirmed this practice as a multi-generational problem, as the U.S. is approaching twenty-five years of depending on an IHL argument that is not legally sound. Rather, this approach is corroding very important distinctions at the backbone of IHL and abusing this language to justify unlawful uses of force. Now Biden, like his predecessors, has an opportunity to confront this issue—but how?

Thoughts for the Future

Two distinct efforts must be made to achieve this aim. First, U.S. policy must realign itself with the substance of international law. Decades of finagling IHL jargon to justify its unlawful armed attacks has resulted in the U.S. essentially gaslighting its enemies, its allies, and international legal scholars. The most important change the U.S. can make here is—granted, easier said than done—to stop mischaracterizing its behavior as compliant with IHL. The second effort is to address the creeping reality that international law does not presently contain the linguistic instruments necessary to engage with contemporary armed conflict—and confronting this issue is not only a task for U.S. foreign policy. Addressing this gap is a task for the international legal community, and it requires acknowledging that our traditional tools for IHL are in desperate need of modernization.


Christine Carpenter is a law student at the University of Pennsylvania with research interests in international judiciaries, human rights law, and counterterrorism policy. She holds a master’s degree in International Relations and Politics from the University of Cambridge and a B.A. in International Affairs and French from Lafayette College.