If a Chinese ship was to open fire on a Philippine coast guard vessel in the disputed South China Sea, what would the United States do? Clearly, given that the Philippines and the United States share a long-standing mutual defense treaty, American forces would be obligated to come to the aid of the vessel if the attack occurred in recognized Philippine territorial waters. But until Manila and Washington issued new bilateral defense guidelines in May 2023, it was unclear what America’s obligations would be if the attack occurred in disputed waters or against non-military Philippine government vessels, like those of its coast guard. Such circumstances were considered “gray-zone” scenarios.

The newly issued bilateral defense guidelines cleared up the ambiguity. They also marked a change in American policy in the South China Sea from “scrupulous noninvolvement” to one that seems focused on deterrence. For the Philippines, the change could not have come soon enough. China’s increasingly aggressive efforts to assert its sovereignty over the waters within its “nine-dash line” in the region have strained the Philippine government’s ability to respond. But the reason why that ambiguity lasted as long as it did was, in part, purposeful. For decades, Washington had been concerned that Manila might be tempted to use the 1951 United States-Philippines Mutual Defense Treaty (MDT) as leverage to advance its maritime and territorial claims against its neighbors, potentially drawing the United States into confrontations with them, most notably China.

In fact, America’s strategic calculus had already begun to shift in the early 2010s. Barack Obama’s administration was the first to take a slightly firmer stance in the South China Sea. Then, American policy took on a more defiant tone under President Donald Trump, who formally rejected China’s “nine-dash line” claim. And with relations between China and the United States deteriorating further during the early years of the Biden White House (not to mention continued Chinese assertiveness in Southeast Asia), Washington had become open to clarifying the terms of its MDT with Manila. Thus, when Philippine President Ferdinand Marcos, Jr. visited Washington in May 2023, he was able to secure what his predecessors had not: a clarification of America’s obligations in “gray-zone” scenarios.

Bilateral Defense Guidelines

As “ironclad” and useful as the MDT has been since its inception in 1951, it was crafted with the circumstances of the Cold War in mind. Its authors could not have imagined the sorts of gray-zone scenarios that would emerge in the South China Sea decades later. Unsurprisingly, some of the treaty’s original terms had become ambiguous in modern situations. Thus, clarification of those terms in the newly issued bilateral defense guidelines constituted a practical change in American policy in the region. In that regard, their most noteworthy provisions include:

Agreement on the conditions for mutual defense. “An armed attack in the Pacific, to include anywhere in the South China Sea, on either Philippine or U.S. armed forces—which includes both nations’ Coast Guards—aircraft, or public vessels, would invoke mutual defense commitments under Article IV and Article V of the MDT.” This guideline means that not only would American forces come to the aid of their Philippine counterparts, but also they would do so in many of the gray-zone scenarios that are more likely to transpire today.

Recognition of the Permanent Court of Arbitration decision. “The United States and the Philippines reaffirm the importance of the 2016 Arbitral Award on the South China Sea.” This guideline refers to the legal case that the Philippines brought against China at the Permanent Court of Arbitration. The court ruled that China had “no legal basis” to claim historic rights within its “nine-dash line” claim and that China had violated the Philippines’ sovereign rights in its exclusive economic zone. Though the guideline stopped short of stating whether Washington believes the court ruling is binding, it does go a bit further than its earlier refutation of China’s claims.

Agreement to adapt to Chinese tactics. The Philippines and the United States would also cooperate to address “asymmetric, hybrid, and irregular warfare and gray-zone tactics.” This guideline means that even if China tries to fashion new “gray zones,” the two countries would act to counter them.

The guidelines also included a significant, if self-referential, provision that “the bilateral Defense Guidelines are not intended to create rights or obligations … and are meant to serve as a living document” that the Philippines and the United States can mutually agree to modify later. In other words, the guidelines are not meant to exceed what is already detailed in the MDT, but could be jointly altered to adapt to new situations as they arise.

Philippines’ External Defense Revival

The earlier ambiguity around America’s MDT obligations gave China room to pressure the Philippines’ South China Sea claims in gray-zone scenarios with reduced risk of American intervention. The main reason for Washington’s opaque posture had been Manila’s longtime neglect of its external defense capabilities. The Philippines, which at one time fielded one of Asia’s largest and most modern armed forces, had allowed its navy to dwindle to four offshore patrol boats and its air force to mothball its last jet aircraft in 2005, even as China conducted a massive military buildup in the region. If Manila was not committed to its own self-defense, Washington was disinclined to shoulder the entire burden for the Philippines.

Hence, the Philippines had become completely dependent on its mutual defense treaty with the United States for its external defense. The situation not only constrained the strategies that Philippine leaders could devise to counter Chinese actions in the South China Sea, but also raised the possibility that Manila, lacking any other means, might use the MDT as leverage to advance its maritime and territorial claims against its neighbors in the region. Naturally, that had the potential of drawing the United States into confrontations with those neighbors, particularly China. Worse still, it could happen at a place and time not of Washington’s choosing.

Officials in Manila well understood how lengthy and expensive (both in terms of financial and political capital) it would be to modernize the Philippine armed forces. Most shrank from the challenge. Former President Gloria Macapagal Arroyo sought to ease Chinese pressure another way—by striking a deal with it. Unfortunately for her, she inadvertently weakened Philippine sovereignty in the process. It was not until Benigno Aquino III became president in 2010 that Manila took its first real steps to revive its navy and air force. It would eventually take him years to pass the legislation required to reform the military and its procurement process so that it could conduct long-term planning and more efficiently acquire new hardware.

Aquino’s multi-phased military modernization program had just gained traction when Rodrigo Duterte entered office. And though Duterte intimated that he would push military procurement towards Russia, he ultimately did not tinker much with it. Thus, in the late 2010s, the Philippine Navy received its first purpose-built frigates and the Philippine air force its first new jet fighters. In 2022, the Philippines even acquired Brahmos ground-launched anti-ship missile systems from India as a cost-effective means to project power into the South China Sea. Ultimately, Manila’s renewed commitment to its external defense capabilities were a key factor in convincing Washington that the Philippines could be a meaningful security partner and worthy of shared defense commitments.

Change in American Strategic Sentiment

To be sure, other actions Duterte took while in office did little to encourage the United States to clarify its policy of ambiguity in the South China Sea, despite the region’s growing importance to Philippine energy security. His very public announcement, during a 2016 visit to Beijing, of the Philippines’ “separation” from the United States was hardly helpful. However, other forces were at work. Many American policymakers had become increasingly disillusioned with the notion that engagement with China would make it less adversarial. Together with China’s growing threat to both America and its Asian allies, relations between China and the United States deteriorated, a trend that accelerated during the Trump administration.

Russia’s invasion of Ukraine in 2022 further dented American relations with China, which chose to provide Russia with dual-use military assistance and reportedly agreed to supply it with even more lethal aid. In late 2022, China’s intimidation of Taiwan soured relations further. That intimidation continued into 2023 when China launched ballistic missiles into the waters around Taiwan and conducted large-scale military exercises around it. China’s display of firepower appeared to persuade American policymakers of the need to seriously prepare for the possibility of a Chinese invasion of Taiwan.

Certainly, the Philippines’ proximity to Taiwan makes Philippine military bases highly valuable to the United States in the event of an armed conflict between it and China over Taiwan. That, ultimately, may have been the final push needed to make Washington amenable to Manila’s desire for clarification of American policy in the South China Sea, perhaps in exchange for expanded access to Philippine bases. In fact, in February 2023, the Philippines agreed to grant the United States access to four additional bases under their Enhanced Defense Cooperation Agreement. And it turns out that three of the four bases are situated in northern Luzon, near Taiwan.

New American Policy Shift

For much of the early 2000s, the United States (and the rest of Asia) had hoped that China would take a less confrontational approach to its maritime and territorial disputes in the South China Sea, perhaps even channeling its claims through multilateral organizations like ASEAN. When it became apparent that would not happen, Washington began to incrementally shift away from long-held policy of “scrupulous noninvolvement” and take steps toward a firmer stance. In 2014, it published maps that cast doubt on China’s “nine-dash line” claim, and a year later resumed the U.S. Navy’s freedom of navigation patrols near Chinese outposts in the region. Against a backdrop of deteriorating relations between China and the United States over trade, cyber espionage, the COVID-19 pandemic, and China’s tightened grip over Hong Kong, the United States then defiantly rejected China’s “nine-dash line” claim in 2020.

The recent clarification of defense obligations under the MDT marked another shift in American policy in the South China Sea to one that seems focused on the deterrence of further provocative Chinese actions. Of course, clarity is crucial for the success of any deterrent strategy. But what is also important is consistency. Beijing may yet test the new bilateral defense guidelines or find new “gray zones” in their language to further challenge Manila in the South China Sea. If deterrence is to succeed, American policy must also be consistent, holding its course in the possible storms to come.

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The views expressed in this article are those of the author alone and do not necessarily reflect the position of the Foreign Policy Research Institute, a non-partisan organization that seeks to publish well-argued, policy-oriented articles on American foreign policy and national security priorities.

Image: Defense Department (Photo by Henry Villarama)