Does the Houthi Blockade Trigger Self-Defense Rights Under International Law?

The narrow question is not whether Houthi attacks have made shipping unsafe. It is whether, when a merchant vessel is struck, the incident becomes an armed attack on the flag State for Article 51 purposes. Warship attacks sit on relatively firm ground; merchant-vessel attacks do not.

The warship baseline is not the hard part

There is little serious doubt that attacks on naval warships can support self-defense. The ICJ's Oil Platforms judgment did not unsettle that baseline, but it also did not answer the harder merchant-vessel problem.[1]

That matters because the legal threshold is gravity, not just hostility. A merchant ship can be the victim of serious wrongdoing without automatically turning the incident into an armed attack on the flag State.

How the U.S. and U.K. framed the strikes

The contemporary operational theory comes through most clearly in the AJIL analysis of the U.S. and U.K. strikes. It describes a self-defense justification tied to the protection of shipping and to UNSCR 2722's deliberate choice not to endorse one legal theory over another.[2][3]

That is a useful signal precisely because it is modest. The Council took note of the right to defend vessels, but the text was drafted so that both restrictive and expansive readers could claim some room under it.[3]

The merchant-vessel question remains contested

The real dispute begins here. The U.S. position has been expansive since the Tanker War: repeated attacks on commercial shipping can be treated as armed attacks on the flag States whose vessels are hit. Frostad treats that move as the central problem rather than a settled answer.[4]

Papastavridis surveys the same terrain and shows why the restrictive view still matters. Bothe and Gray are part of the line of scholarship that says one merchant-vessel strike does not obviously satisfy the gravity threshold that a warship attack does not test.[5]

That difference is not semantic. If a single merchant-vessel strike is enough, Article 51 expands quickly at sea. If it is not, states may still respond, but they should be careful about calling every protection mission self-defense.

That debate sits inside a real chokepoint. Once traffic shifts away from the Bab el-Mandeb and Suez corridor, the legal argument stops being academic for shipowners, insurers, and naval planners.

Domestic law shadows the same dispute

The domestic-law shadow runs alongside the international-law one. Congressional Research Service materials note that the War Powers Resolution question remains unresolved, and the 60-day period passed in March 2024 without extension.[6] Senator Kaine's February 2024 letter put the practical complaint plainly: if the strikes rest on self-defense but not on congressional authorization, what is the domestic hook?[7]

The May 2025 ceasefire and the resumption of attacks in March 2026 only make the factual setting harder to freeze in place.

Where the law stands now

The restrained conclusion is the most defensible one. The U.S. has a real and operationally important self-defense theory for strikes tied to merchant-ship protection, but the scholarly consensus is still missing, and UNSCR 2722 was written in a way that can live with both restrictive and expansive readings.[2][3][4][5] That leaves the legality of future U.S. and U.K. operations dependent on how hard a lawyer wants to press the merchant-vessel analogy, and on whether the record at the time can bear the gravity claim.

References

1. Oil Platforms (Islamic Republic of Iran v. United States of America), International Court of Justice, 2003
2. AJIL analysis of the U.S. and U.K. strikes on the Houthis, Cambridge, 2024
3. UN Security Council Resolution 2722, United Nations Security Council, 2024
4. Self-defense and merchant vessels, Lieber Institute
5. The Houthi attacks and the law of self-defense, ELIAMEP
6. Houthi attacks and the War Powers Resolution, Congressional Research Service
7. Letter to President Biden on strikes in Yemen, Senator Tim Kaine, February 2024