As the United States and China volley round after round in an escalating trade war, a second front of conflict is brewing in the contested South China Sea, one that could soon force smaller regional states to take geopolitical sides.

This week, a US Navy guided-missile destroyer was deployed near the Scarborough Shoal, a sea feature occupied by China since 2012 but claimed by the Philippines as part of its exclusive economic zone (EEZ).

The deployment was the destroyer’s second freedom of navigation operation (FONOP) near the shoal this month, maneuvers which pointedly challenge China’s recent militarization of the features it controls in the waterway.

The sea maneuver came against the backdrop of joint US-Philippine coast guard exercises held earlier this month near the Scarborough Shoal, the two sides’ first ever search-and-rescue exercise near the feature.

Chinese coast guard ships closely monitored the exercise, coming within five kilometers of a Philippine ship participating in the drill. Beijing has cause for concern: US and Philippine forces held a joint drill in April that simulated re-taking a remote occupied island. Some believe the exercises signal a bigger future role for the US Coast Guard in the area.

This year, China has doubled down on its military and para-military deployments in the South China Sea, prompting concerns about potential clashes with smaller claimant states.

Chinese President Xi Jinping reviews a military display of Chinese People’s Liberation Army Navy in the South China Sea on April 12, 2018. Photo: Xinhua

China has territorial disputes with the Philippines, Vietnam, Malaysia, Indonesia and Taiwan in the broad maritime area. Beijing claims as much as 90% of the sea in a so-called “nine-dash line” map.

In response, US President Donald Trump’s administration has announced it will unveil a new strategy to combat China’s maritime ambitions at the forthcoming Shangri-La Dialogue (May 31-June 2) in Singapore. US Secretary of Defense Patrick Shanahan is scheduled to make an address at the conference.

There are already signs of growing naval coordination among US-aligned nations.

For the first time, the US, Japan, India and the Philippines conducted (May 9) joint FONOP exercises in route to Singapore for the second phase of the Association of Southeast Asian Nations (ASEAN) Defense Ministers Meeting Plus Maritime Security Field Training Exercise.

The Philippine Navy’s BRP Andres Bonifacio (PS-17) cutter joined warships from allied nations, namely the US Navy’s USS William P Lawrence (DDG-110), Japan’s JS Izumo (DDH-183) and JS Murasame (DD-101), and India’s INS Kolkata (D63) and Shakti (A57).

While the four countries have held joint exercises in various bilateral and trilateral permutations in recent years, it was the first time that they mounted joint forces to signal a shared commitment “to promote maritime cooperation throughout a free and open Indo-Pacific.”

The Philippine Navy, long the region’s laggard, is now undergoing a once-in-a-generation modernization drive to upgrade its equipment and capacities. China’s assertive moves in Philippine-claimed waters can be attributed in part to Manila’s naval vulnerabilities.

Philippine officials were upbeat about the exercises, even as they clearly riled China. Captain Roy Vincent Trinidad, the Philippine Navy’s head of delegation, said the exercises “gives us another opportunity to learn from like-minded navies.”

Under President Rodrigo Duterte, the Philippines has pursued warmer ties with China.

But the festering disputes in the South China Sea – with Beijing deploying hundreds of para-military vessels in the vicinity of Philippine-held land features, namely the strategic Thitu Island – has compelled his government to quietly upgrade security cooperation with its US treaty ally.

The two sides are expected to officially review their 1951 Mutual Defense Treaty, which compels each side to come to the others’ defense in the case of an attack, later this year.

Many in the Philippine defense establishment felt the US should have been more forthright with its treaty obligations when China seized control of the Scarborough Shoal after a months-long naval standoff in 2012.

With China’s creeping presence in the area, Philippine defense officials want stronger US security assurances. Indeed, Defense Secretary Delfin Lorenzana told this writer on May 1 that he was “dead serious” about assessing the future utility of the country’s American alliance.

The review process will likely seek to introduce new guidelines for the treaty in order to address China’s emerging “gray zone” strategy of deploying para-military forces to swarm, surround and suffocate land features occupied by smaller claimant states.

Philippine Defense Secretary Delfin Lorenzana gestures at the military headquarters of Camp Aquinaldo in Quezon city, metro Manila, Philippines February 9, 2017. Photo: AFP

China’s provocations vis-a-vis the Philippines and other claimants are galvanizing a wider Western response. Last month, for instance, the French Navy conducted its own FONOP in the South China Sea, including in the Taiwan Straits.

The maneuver prompted an angry response, with China’s Defense Ministry spokesman Ren Guoqiang accusing the French warship, the Vendemiaire, of “illegally enter[ing] China’s territorial waters.”

The French frigate then failed to show up as scheduled for the international naval parade commemorating the 70th anniversary of China’s People’s Liberation Army Navy (PLAN). Paris did not provide an explanation for the apparent snob, though Australian and Indian warships participated.

There are likely more such moves on the horizon. US Assistant Secretary of Defense for Indo-Pacific Security Affairs Randall Schriver recently told a media roundtable in Kuala Lumpur that the “Indo-Pacific” has become America’s global “priority theater.”

“And over time you will see that show up in resources and presence, though I’m not in a position to talk on the specifics of that,” he added, saying Shanahan will elaborate on the strategy at the upcoming Shangri-La Dialogue.

The Pentagon official told the USNI News during the conference that the strategy’s aim is to ensure China “will not deploy additional military systems and in fact remove the military systems” it has deployed to artificially created islands in the South China Sea.

“[I]t’s our intent to make sure that no one country can change international law or the status of the South China Sea, so that’s why we conduct the [FONOPs] and the other presence operations in the South China Sea.”

The aircraft carrier USS Carl Vinson transits the South China Sea. Photo: US Navy Handout

Those operations include daily US Air Force patrols over the South China Sea to ensure freedom of overflight, according to Charles Brown Jr, the force’s Pacific commander, told a news briefing last week in Manila. “I realize that, sometimes, you know, China does not like that fact.”

Washington seems increasingly confident that it can get the support of more like-minded countries to collectively constrain China’s ambitions for the sea area, including the possible establishment of an Aerial Defense Identification Zone (ADIZ).

“We’re joined by a lot of countries who see the potential erosion of international law as a problem not only in the South China Sea but [with] broader implications,” Schriver said.

That message will resonate in certain Philippine quarters, significantly at a time Beijing is taking hard aim at Filipinos who have spoken out against its perceived aggression in the South China Sea.

Conchita Carpio Morales, a former Philippine Supreme Court justice who accused Chinese President Xi Jinping of crimes against humanity at the International Criminal Court over his South China Sea policies, was detained and interrogated on Tuesday for four hours at Hong Kong’s airport.

The Philippines won an arbitral award against China’s wide-ranging claims to the South China Sea at a tribunal at The Hague in July 2016. Until now Duterte’s government has not pressed Beijing to honor the award, which Beijing has said has no legal standing or enforcement mechanism.

But with more US naval vessels and air force planes headed for the maritime region, that may soon change.