It is an article of faith among ordinary Filipinos that American troops will die with Filipino troops defending Philippine claims to the Spratly Islands in the South China Sea (SCS). Even Filipino scholars profess this view. US-Philippine military exercises simulated the recapture of an SCS island. The Philippine government believes in the “solid commitment of the United States [U.S.]” to defend Philippine sovereignty in the Spratly Islands through “interoperability” between their forces in countering China. It has allowed in Philippine territory prepositioned U.S. military equipment and personnel under an Enhanced Defense Cooperation Agreement.

Does the U.S. have an obligation to defend the Philippines in the SCS under their Mutual Defense Treaty (MDT)?

Ambiguity by Design

The recent statements of the U.S. government are ambiguous. “[A]ny attack on Philippine aircraft, vessels, or Armed Forces in the South China Sea would invoke our mutual defense treaty,” U.S. President Joe Biden said during the first U.S.-Japan-Philippines Trilateral Summit on April 11, 2024. U.S. Secretary of State Anthony Blinken declared that Americans “stand[s] by our ironclad defense commitments, including under the Mutual Defense Treaty [MDT]… [which] extends to armed attacks on the Filipino armed forces, public vessels, aircraft – including those of its coast guard-anywhere in the South China Sea.” U.S. Defense Secretary Lloyd Austin reiterated that the MDT “extends to both countries’ armed forces, public vessels, and aircraft-including those of its Coast Guard-anywhere in the Pacific, including the South China Sea.”

The scope of the territorial and maritime disputes in the South China Sea was clarified in the 2016 SCS Arbitration between the Philippines and China. According to the Arbitral Tribunal, the Spratly Islands consist of low-tide elevations not susceptible to appropriation and high-tide elevations that are not islands but rocks and entitled only to a 12-nautical-mile territorial sea. China, Malaysia, Philippines, Taiwan, and Vietnam claim these rocks, but none may treat the rocks as an offshore archipelago.

Taiwan, Vietnam, and Malaysia are American allies, although not at the level of mutual defense that the Philippines enjoys with the U.S. Taiwan recently received U.S. military funding. In 1975, upon the advice of the U.S. but “over strong objection of [Filipino] navy and marines,” the Philippines “[withdrew] from … Likas (West York)” to give way to Vietnamese forces, whose presence the U.S. preferred to the “boot-shaking prospect of having to face PRC alone at some future date over Spratlys.”

Thus, the question arises as to whether U.S. “ironclad commitment” under the MDT applies in an armed conflict involving the Philippines against China and other claimants in the SCS.

1975 U.S. Legal Interpretation of the MDT

Under Article V, the MDT covers 1) an external armed attack on a “metropolitan territory or an island territory in the Pacific” under the jurisdiction of either party; and 2) an armed attack on the “armed forces, public vessels or aircraft in the Pacific” of either party.

As early as 1975, then-U.S. Secretary of State Henry Kissinger issued a memorandum-telegram laying down the “legal interpretation of MDT commitments” that  U.S. commitments “do not repeat do not apply in event of attack on Spratlys or attack on GOP [Government of the Philippine] forces stationed there.” It cited two grounds: first, the Spratly Islands are not part of Philippine territory; and second, the Philippines is not a claimant in respect of the Spratly Islands.

In its 1975 legal interpretation, the U.S. declared that it has not “recognized GOP sovereignty” over these islands. During the MDT negotiation and ratification in 1952, in the mind of the U.S. the “Spratly Islands all fall outside Philippine territory as ceded to U.S. by 1898 Treaty with Spain;” consequently, “U.S.G. [U.S. Government] maps accompanying presentation of MDT also exclude Spratlys from territories covered by MDT.”

In the same 1975 legal interpretation, the U.S. designated the 1951 negotiations on the Japanese Peace Treaty as the critical date for the purpose of identifying the claimants to the Spratly Islands. It declared that “at the time the MDT [was] signed, {Philippines] had asserted no claim to any of the Spratly Islands and had protested neither Vietnamese nor Chinese claims.” Rather, “at time of negotiation of 1951 Japanese Peace Treaty,” specifically the provision on the status of the Spratly Islands, only China and Vietnam interposed claims. Thus, even as the U.S. did not favor any of the claimants to the Spratly Islands, it did not consider the Philippines as one of them.

1979 U.S. Legal Interpretation of the MDT

Nonetheless, in 1978, the Philippines formally claimed the Spratly Islands as an offshore archipelago arguing that “while other states have laid claims to some of these areas, their claims have lapsed by abandonment and cannot prevail over that of the Philippines on legal, historical, and equitable grounds.” Still, then-U.S. Secretary of State Cyrus Vance did not declare the MDT applicable to the disputed Spratly Islands. Rather, Document 578 of American Foreign Policy Basic Documents 1977-1980 is a 1979 letter to then-Philippine Minister of Foreign Affairs Carlos Romulo, in which Vance further clarified the U.S. legal interpretation of the MDT. He declared that armed attack under the MDT refers to external armed aggression against any part of Philippine metropolitan territory as defined by the 1898 Treaty of Paris between Spain and the U.S. and the 1900 Treaty of Washington between Great Britain and the U.S. (amended in 1930), as well as island territories in the Pacific that are under Philippine jurisdiction. Moreover, “armed attack on any Philippine armed forces, public vessels or aircraft in the Pacific would not have to occur within the Philippine metropolitan territory or island territory under its jurisdiction in the Pacific in order to come within the definition of Pacific Area in Article V.” Thus, armed attack on said forces or vessels taking place in undisputed maritime areas in the South China Sea would fall within the scope of the MDT.

Melissa Loja is a Postdoctoral Fellow at University of Copenhagen. She is the author of “International Agreements between Non-state Actors as a Source of International Law” (Hart, 2022) and various journal articles in the European Journal of International Law, the International Journal of Constitutional Law and the Leiden Journal of International Law.

Romel Regalado Bagares is a professorial lecturer in international law in three Manila-based law schools and the Philippine Judicial Academy. His latest publication (with José Duke Bagulaya), ‘Hidden in Plain Sight: International Law and Marxist Praxis in the Life and Works of Merlin M. Magallona’ was published in the Asian Journal of International Law.

Read more on Asian law topics in the Asian Journal of International Law.