The Biden Doctrine?: The February 25 Airstrike in Syria, Article 51, and the Future of International Law in the Biden Administration

The Biden Doctrine?: The February 25 Airstrike in Syria, Article 51, and the Future of International Law in the Biden Administration

The February 25 Airstrike in Syria

In a June 2016 interview, then-Vice President Joe Biden cast doubt on the utility of interventionist foreign policy. Citing the shortcomings of the 2011 NATO-led military intervention in Libya, Biden stated that he was “strongly” against the intervention. In reference to the ouster of Libyan leader Muammar Qadhafi, Biden said, “He’s gone. What happens? Doesn’t the country disintegrate? What happens then? Doesn’t it become a place where it becomes a Petri dish for the growth of extremism? Tell me. Tell me what we’re gonna do.”

One month after Joe Biden was sworn in as President, the United States conducted an airstrike in eastern Syria. The February 25, 2021, strike was reportedly in response to a February 15 rocket attack on the airport in Erbil, Iraq by the Iranian-backed Awliya al Dam militia which killed a contractor and wounded six other soldiers and contractors. While Pentagon spokesman John Kirby characterized the strike in Syria as “proportionate” and “defensive” in nature, unconfirmed reports by the monitoring organization Syrian Observatory for Human Rights indicated that at least 22 people were killed. Authorized by the President, and the first military operation of the Biden administration, the strike offers an early look at the “Biden Doctrine” of foreign policy and international relations.

The February 27 Letter

In a February 27, 2021, letter from the White House to Congressional leaders, Biden called the February 25 action a “targeted military strike against infrastructure . . . used by Iran-supported non-state militia groups.” The letter was significant for several reasons. First, unlike similar documents from the Trump administration, it was immediately made public, creating greater transparency for the administration and the strike. More importantly, the legal basis for the intervention as told to Congress—and for the entire world to see—was based not just in U.S. constitutional law, but on principles of international law and international humanitarian law (IHL).

Justifying this military intervention using international law represents a significant departure from past rationales for military action in Syria. The legal justification for a 2017 airstrike in Syria remains classified. But an April 2018 Department of Justice Office of Legal Counsel memorandum claimed that the legal basis for that airstrike targeting Syrian chemical weapons facilities was that the use of force was in the “national interest” and consistent with the president’s war powers because it did not rise to “war in the constitutional sense.”

In contrast, while the February 27 letter only briefly touched on President Biden’s constitutional authority under Article II to conduct foreign relations and duty to protect U.S. citizens abroad, the centerpiece of the legal case for the strike was the United States’ “inherent right of self-defense” enshrined in Article 51 of the UN Charter. In addition, the letter characterized this act of self-defense as both “necessary and proportional,” signaling compliance with the customary IHL rule on proportionality in attack and the overarching IHL principle of military necessity. Likewise, the letter also pointed to the “unwilling or unable doctrine,” where a State may lawfully use force against a non-state actor (NSA) within the territory of a third State if the third State is unwilling or unable to deal with the NSA. It is unclear whether the unwilling or unable doctrine has risen to the level of customary international law, but more on that shortly. While use-of-force justifications built upon each of these international law principles warrants examination, the invocation of Article 51 by the U.S. is rare enough that it requires special attention.

Article 51 of the UN Charter

Save for authorization by the UN Security Council (UNSC), the threat or use of force is generally prohibited under UN Charter Article 2(4). However, UN Charter Article 51 preserved the right to self-defense. Article 51 states:

Nothing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations, until the Security Council has taken measures necessary to maintain international peace and security. Measures taken by Members in the exercise of this right of self-defence shall be immediately reported to the Security Council and shall not in any way affect the authority and responsibility of the Security Council under the present Charter to take at any time such action as it deems necessary in order to maintain or restore international peace and security.

While Article 51 was arguably a codification of a right “inherent” to all States, it does impose an additional requirement upon any State engaging in self-defense: reporting the use of force to the UNSC. Professor James Green posits that the initial purpose of the reporting requirement was to “centraliz[e] the use of military force with the newly created [UNSC] following the atrocities of World War II.” The goal was to give the UNSC the ability to scrutinize claims of self-defense.”

History of U.S. Invocation of Article 51

To say that the United States has been inconsistent in invoking Article 51 would be an understatement. In 2019, the Harvard Law School Program on International Law and Armed Conflict (PILAC) catalogued Article 51 communications to the UNSC regarding measures taken in self-defense and determined that the Article was invoked 433 times from 1950 to 2018. According to the study, the United States invoked Article 51 only four times in the last twenty years: in connection to military action related to the September 11, 2001, terrorist attacks, the 2003 invasion of Iraq, the 2014 Benghazi compound attack, and the 2014 ISIS/ISIL operations. Over that same period, the United States was the “author” (or belligerent) of an Article 51 threat in 61 communications to the UNSC. Meanwhile, the Congressional Research Service estimates that the U.S. military has been deployed to dozens of foreign countries in discrete overseas operations over that same period.

Was the February 25 Invocation of Article 51 Consistent with International Law?

As an initial matter, the United States communicated its use of force and its invocation of Article 51 to the UNSC in a February 27, 2021, letter. Like the letter from President Biden to Congressional leaders, the public UNSC letter stated that the airstrike was “necessary and proportionate” and declared that Syria was “unable or unwilling” to prevent the use of its territory by NSAs for attacks.

But outside of the United States meeting the reporting requirement, was the actual use of force in Syria consistent with Article 51 self-defense? It should come as no surprise that this has sparked intense debate among international law scholars.

Professor Adil Ahmad Haque argues that the airstrikes in Syria violated international law, writing that they “did not repel an ongoing armed attack, halt an imminent one, or immediately respond to an armed attack that was in fact over but may have appeared ongoing at the time.” Further, the militia group that claimed responsibility for the rocket attacks in Erbil was not targeted, indeed the “self-defense” that took place occurred in an entirely different country. Perhaps most importantly, Haque rejects the central thesis of the unwilling and unable doctrine, writing “the airstrikes were carried out on the territory of another State, without its consent, against a non-State actor . . . [i]t cannot be lawful to use armed force on the territory of another State when it is clear that no armed attack” is ongoing by an NSA. Indeed, if Haque is correct, particularly regarding the attenuation between the initial attack (which killed one person) and the Syrian airstrike (which reportedly killed almost two dozen people), then the February 25 strike looks more like an illegal reprisal than self-defense. 

But what if the law of self-defense is, as Professor Ryan Goodman writes, “less clear cut than some other critics have suggested?” Leaving aside the thorny issues of the unwilling or unable doctrine, and the fact that the attack took place in Syria, Goodman argues that instead of conceptualizing the Erbil attack as “clearly over and not ongoing,” one could think of it as part of a series of “recurring attacks.” And if a State can predict with “high confidence” that a “proportionate military strike” might end that threat, might self-defense extend to this action? Goodman cites evidence from Roberto Ago, Special Rapporteur for the UN ILC, and Brian Egan, former State Department Legal Adviser, that self-defense can extend to the “prevent[ion] and deter[rence of] further attacks.” While Goodman does not come to a conclusion about whether the February 25 strike was consistent with international law, his analysis, if correct, certainly cuts away from describing the strike as a reprisal.

What Does This Mean for International Law?

After four years of what Professor Oona Hathaway called “President Donald Trump’s rejection of international law,” one’s initial reaction to the February 27 letters might be to commend the Biden administration for even making the effort to justify a military strike through the framework of international law and Article 51. But some healthy skepticism may be warranted.

International law as a regime is uniquely shaped by its actors, even at the level of the individual. Indeed, Article 38(1)(d) of the Statute of the International Court of Justice says that the Court should apply “teachings of the most highly qualified publicists” alongside “judicial decisions” as a subsidiary means to resolving disputes. Nowhere is the power of the actors in the system more apparent than in the development of customary international law (CIL). CIL is “a general rule,” binding on all states, and its development requires two things: uniform state practice and opinio juris. Opinio juris “denotes a subjective obligation, a sense on behalf of a State that it is bound” by law to take the action in question. Opinio juris can take many forms, from informal speeches by public officials to official government press releases. The two February 27 letters certainly qualify as an official government statement of what the law is. In other words: By justifying his actions within the framework of international law, President Biden is actively shaping the law—something that President Trump either failed to grasp or just plain didn’t care about doing.

For example, according to Postdoctoral Fellow Elena Chachko and Professor Ashley Deeks, in 2016 ten States “explicitly endorsed” the unwilling or unable doctrine, with only six States objecting to it as a rule. To greatly oversimplify the debate: Every justification for intervention premised on the unwilling or unable doctrine builds a stronger case that it is, or will become, CIL. This context is important considering that recent presidential administrations have insisted that acts inconsistent with international law, like torture and targeted killings, are totally legal.


Outside of this discussion about Article 51 and the airstrike in Syria, many questions remain about President Biden’s approach to military interventions and whether his administration will continue to use—and shape—international law in justifying such acts. Will he adopt the view put forward by Samantha Power, the former U.S. Ambassador to the United Nations and Biden’s nominee for USAID Administrator, that the United States has a “responsibility to protect” the powerless from mass atrocity crimes? Or did Biden learn a noninterventionist lesson from the ostensibly “humanitarian” intervention in Libya in 2011? Will the February 25 strike preclude the United States from reentering the JCPOA, further chill relations with Iran, or prevent the United States from addressing the prior administration’s “maximum pressure” sanctions campaign? As then-Vice President Joe Biden said in that 2016 interview: “Tell me. Tell me what we’re gonna do.”


Dylan Helgeson: Executive Editor, California Law Review, Vol. 109, Berkeley Law Class of 2021.

Dylan Helgeson, The Biden Doctrine?: The February 25 Airstrike in Syria, Article 51, and the Future of International Law in the Biden Administration, Calif. L. Rev. Online (May 2021),

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