On March 31, the U.S. think tank Center for Strategic and International Studies (CSIS) published a commentary titled The Ripple Effects of Vietnam’s Island-Building in the South China Sea, authored by Harrison Prétat, Deputy Director of CSIS’s Asia Maritime Transparency Initiative (AMTI) and a senior fellow. Prétat previously co-authored an environmental assessment report titled Deep Blue Scars, published in December 2023 by CSIS, accusing China and Vietnam of "accelerating the destruction of coral reefs in the South China Sea." In his latest commentary, Prétat concisely analyzes Vietnam’s large-scale island-building activities since 2021 and correctly notes that such construction "does nothing to change the nature of Vietnam’s territorial and maritime claims, or the legal status of the features themselves."

Earlier, on March 21, AMTI had published an anonymous feature titled Scaling Up: Vietnam’s Islands (and Harbors) Continues to Grow, which included multiple satellite images and provided a more detailed analysis of Vietnam’s ongoing reclamation efforts. However, Prétat’s latest commentary appears to have ulterior motives—its true purpose is not merely to rehash Vietnam’s island-building activities but to use the supposed "ripple effects" of Vietnam’s actions to advise another South China Sea claimant, the Philippines. The underlying goal is to pressure China through potential Philippine "legal actions," forcing China to yield to U.S. criticisms of its maritime claims.

Since the second half of 2024, Philippine officials have repeatedly threatened to initiate a new arbitration against China over environmental issues in parts of the South China Sea. In January, Philippine Justice Secretary Crispin Remulla confirmed in an interview with Reuters that the Philippines would to pick venue soon for second South China Sea case against China. However, Prétat argues that targeting China solely over environmental issues is not an "appealing option". Based on his own "environmental assessment" reports and research, Vietnam’s island-building has also caused significant damage to coral reefs. Thus, if the Philippines sues China alone while ignoring Vietnam’s actions, it risks accusations of "double standards," losing the moral high ground and potential international support—hence the "ripple effects" mentioned in his commentary’s title.

In the final paragraph, Prétat suggests: " Manila would be wise to consider the advantages of instead filing a broader case that looks at more than environmental issues. By filing a case that includes arguments against China’s truly exceptional maritime claims, Manila could avoid the appearance of a double standard and make it easier to rally international support for its cause. "

What are China’s "Exceptional Maritime Claims"?

This term is essentially a variation of the U.S. government’s long-standing opposition to what it calls China’s "excessive maritime claims." The U.S. Navy’s "Freedom of Navigation Operations" (FONOPs) in the South China Sea are based on this premise. However, while FONOPs typically challenge maritime claims directly related to navigational rights (eg., the innocent passage of warships), Prétat’s "exceptional maritime claims" likely encompass broader issues, possibly including China’s position on the "archipelagic unity doctrine."

According to the Statement of the Government of the People’s Republic of China on China’s Territorial Sovereignty and Maritime Rights and Interests in the South China Sea (July 12, 2016), China asserts that "Nanhai Zhudao (the South China Sea Islands) are entitled to territorial seas, contiguous zones, exclusive economic zones (EEZs), and continental shelves," and that "China’s position is in line with international law and practice." Chinese international legal scholars interpret this as meaning that the four major archipelagos in the South China Sea each form a unified whole, collectively entitled to maritime zones. For example, in May 1996, China delineated baselines around its Xisha Qundao (Paracel Islands) using straight baselines, treating the archipelago as a single unit—a practical application of the "archipelagic unity doctrine." So far, China has only announced baselines for Scarborough Shoal (part of the Zhongsha Qundao) in November 2024 but has yet to do so for the other major archipelagos.

Article 46(2) of the United Nations Convention on the Law of the Sea (UNCLOS) defines an "archipelago" as "a group of islands, including parts of islands, interconnecting waters, and other natural features which are so closely interrelated that such islands, waters, and other natural features form an intrinsic geographical, economic, and political entity, or which historically have been regarded as such." China has consistently maintained since the 1930s that the four major South China Sea archipelagos (Dongsha, Xisha, Zhongsha, and Nansha) each constitute a unified whole, collectively referred to as "Nanhai Zhudao." The 1948 Location Map of the South China Sea Islands published by the Republic of China government further solidified international recognition of these archipelagos. Thus, in China’s point of view, China’s archipelagic claims align with UNCLOS’s definition.

Moreover, nearly 20 continental states—including Western powers like the U.K., France, Spain, Portugal, and Denmark—have drawn straight baselines around their outlying archipelagos, treating them as unified entities. Examples include Denmark’s Faroe Islands (1963), the U.K. and Argentina’s competing baselines for the Falklands/Malvinas (1989 and 1991), France’s Kerguelen Islands (1978) and Guadeloupe (1999), Norway’s Svalbard (1970), Spain’s Canary Islands (1977), Portugal’s Azores (1985), and India’s Andaman and Nicobar Islands (2009). This demonstrates that the "archipelagic unity doctrine" is well-supported by state practice.

U.S. Diplomatic Protest and the Chinese Response
The U.S. government has repeatedly opposed China’s "archipelagic unity doctrine." Official statements such as former Secretary of State Mike Pompeo’s U.S. Position on Maritime Claims in the South China Sea (July 13, 2020) and former Secretary Antony Blinken’s Fifth Anniversary of the South China Sea Arbitral Tribunal Award (July 12, 2021) explicitly criticize China’s maritime claims. In January 2022, the U.S. State Department released Limits in the Seas No. 150: China’s Maritime Claims in the South China Sea, accompanied by a 94-page supplement on state practice and executive summaries in Chinese and Vietnamese, targeting China’s archipelagic stance.

On December 5, 2024, the U.S. Mission to the United Nations submitted two diplomatic notes to the UN Office of Legal Affairs, accusing China’s maritime claims of " are without a factual or legal basis," including objections to the "archipelagic unity doctrine." China’s mission to the UN rebutted these claims in a February 28, 2025, note, reaffirming its position. Subsequently, on March 10, 2025, U.S. allies the U.K., France, and Germany issued a joint note opposing China’s doctrine. China responded on April 8, stressing that "it has long been established in general international law that an archipelago constitutes a legal whole. … The long-established practice regarding continental States' outlying archipelagos in international law should be respected. "

From this exchange of diplomatic notes, it is clear that since the July 12, 2016, South China Sea arbitration ruling—which unlawfully rejected China’s "nine-dash line" and historic rights—the "archipelagic unity doctrine" has become another focal point of U.S.-led "legal warfare" against China’s maritime claims.

A Warning for China
Notably, Paragraph 575 of the 2016 arbitral award explicitly denied that the Nansha Qundao (Spratly Islands) could be enclosed with straight baselines. Although the tribunal did not formally rule on the "archipelagic unity doctrine" (as it was not raised by the Philippines in its submissions), its reasoning leaves room for future challenges. Thus, if the Philippines follows Prétat’s advice and targets China’s doctrine in a second arbitration, it would not violate the legal principle of res judicata.

In short, Prétat’s commentary is a calculated and insidious move. As a U.S. think tank researcher, he is well-attuned to Washington’s policy direction. By framing his advice as an analysis of Vietnam’s actions, he subtly encourages the Philippines to sue China over its "exceptional maritime claims," effectively conveying the U.S. government’s intent to pressure China into abandoning its "archipelagic unity doctrine."

China’s Preparation for the Incoming Legal Challenge
For the Chinese government and academic institutions—especially those specializing in maritime and international law—it is crucial to strengthen theoretical research on the "archipelagic unity doctrine" and prepare for potential "second arbitration" scenarios. By solidifying the legal foundations of China’s South China Sea claims, China can confidently counter Western "legal warfare" and thwart the schemes of think tanks like the CSIS.

As the saying goes, "True gold fears no fire." If China fortifies its legal defenses, no amount of U.S.-orchestrated pressure—whether from Western powers or regional claimants—will shake its rightful maritime claims.

（Author: Dr. Bao Yinan, Associate Research Fellow, Huayang Center for Maritime Cooperation and Ocean Governance)