China was not present, but it was the main protagonist. The first trilateral meeting between the leaders of the United States, Japan and the Philippines on Thursday at the White House sought to provide a show of unity in the face of China’s increasingly intense pressure on Manila in the South China Sea, where the Asian giant claims sovereignty over almost all of the area and maintains a bitter territorial dispute with the archipelago. Washington has described Beijing’s tactics as “intimidation.”

The Philippine and Chinese vessels have engaged in increasingly frequent and hostile skirmishes in an area of the South China Sea that the United States calls the Second Thomas Atoll, and which the Philippines know as the Ayungin Shoal. There, Manila maintains a military garrison in an old, rusty warship — which it intentionally ran aground in the reef — to reinforce its territorial claims in the reef. Chinese ships patrol the area and try to stop the vessels that come to supply it with water cannons and lasers.

The most serious incident in recent weeks took place at the end of March, when Chinese ships fired a water cannon at a Philippine logistics ship that was trying to bring supplies to the military personnel stationed in the shoal, which is located within 200 miles of the Philippines exclusive economic zone. That episode sparked loud protests in Manila, which were backed by Washington. For the United States, Beijing’s tactics amount to coercion and violate international law in waters that are considered one of the most volatile areas on the planet. U.S. President Joe Biden addressed the issue during his telephone conversation with Chinese President Xi Jinping on April 2.

At the start of the trilateral meeting on Thursday, Biden warned that any attack against Philippine forces in the South China Sea would be grounds to apply the mutual defense treaty between Washington and Manila, which was signed in 1951. He said that U.S. forces would come to support its ally.

“I want to be clear, the United States’ defense commitments to Japan and to the Philippines are ironclad. They’re ironclad. Any attack on Philippine aircraft, vessels or armed forces in the South China Sea would invoke our mutual defense treaty,” said Biden.

The president met separately with Philippine President Ferdinand Marcos Jr. shortly before the trilateral meeting. The previous day, he received Japanese Prime Minister Fumio Kishida, who was on a semi-official visit to the White House. The three countries share deep distrust over China’s growing assertiveness in the Asia Pacific and the Asian giant’s territorial claims, which an international court deemed baseless in 2016.

The Philippines and China are in dispute over the South China Sea, while Japan and China have conflicting claims in the East China Sea over islands Japan knows as Senkaku and China identifies as Diaoyu. Manila — which during Rodrigo Duterte’s mandate tried to get closer to Beijing — has resolutely aligned itself with Washington since Marcos’ election. The Philippine president is completing his second official visit to Washington in just over a year.

Tokyo, meanwhile, is investing rapidly in building up its defense in a bid to transform its army into the third most powerful in the world. In their bilateral meeting on Wednesday, Kishida and Biden announced the biggest upgrade to the Japan-U.S. security alliance in more than 60 years. The plan includes greater coordination between their commands and the joint development of cutting-edge military technologies.

“The United States, Japan, and the Philippines are three closely-aligned maritime democracies with increasingly convergent strategic objectives and interests,” White House National Security Advisor Jake Sullivan said on Tuesday.

At the end of the meeting, the leaders said they will announce a Coast Guard patrol in the Indo-Pacific region. The U.S. Coast Guard will also admit members of the Philippine and Japanese corps on these patrols for training, according to senior U.S. officials who spoke on condition of anonymity. Biden also announced the establishment of a new economic corridor in the Philippines for infrastructure development and agricultural projects, among other investments.

This week’s bilateral and trilateral meetings are part of the Biden administration’s efforts to develop a network of economic and security alliances in the Indo-Pacific to respond to China.

“Today’s summit is an opportunity to define the future that we want, and how we intend to achieve it together,” Marcos told the press on Thursday. “This meeting can be just a beginning. Facing the complex challenges of our time requires concerted efforts on everyone’s part, a dedication to a common purpose and an unwavering commitment to the rules-based international order.”

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