TAIPEI, TAIWAN — Within days of President Obama concluding his recent trip to Asia, which was meant to reinforce America’s commitment there as the Chinese threat grows, China attacked Vietnamese vessels to advance its claim over disputed waters and to test Washington’s resolve. A firm, multilateral response is needed to avoid escalation and to demonstrate that China’s combativeness pushes its adversaries together and closer to the U.S.

China has sought to aggressively expand its control of the East and South China Seas, where its claims conflict with those of other countries. Throughout 2011, China harassed Vietnamese fishing and oil exploration vessels. In June 2012, after India and Vietnam agreed to jointly explore oil in the South China Sea, a Chinese navy vessel shadowed Indian ships traveling in international waters between the Philippines and South Korea. In mid-2012, China expelled Filipino ships from the Scarborough Shoal, which is 399 miles closer to the Philippines than China. In November 2013, China expanded its air defense identification zone (ADIZ) to cover parts of the East China Sea claimed by Japan, South Korea, and Taiwan.  In March 2014, China blocked the Philippines from resupplying a ship in disputed territory.

Distracted by budget issues and foreign policy crises outside of Asia, the U.S. took little action against China’s pattern of coercion. Indeed, China aims to press its interests in small increments that do not individually provoke a strong U.S. response. The reason for President Obama’s tour of Asia last month was to demonstrate that America’s security guarantees remain strong. Beijing was unconvinced.

On May 2, just three days after President Obama’s Asia trip, China placed a state-owned oil-drilling rig in contested parts of the South China Sea — 120 miles from Vietnam and 180 miles from China. Vietnamese ships intervened, but some of the 80 or so Chinese vessels accompanying the rig rammed and blasted them with water cannons. A tense standoff persists as Beijing plans to keep its rig there until August 15.

Beijing is gauging Washington’s resolve to stop its creeping expansionism. China seeks in the contested waters more than control of natural resources and a valuable trade passage.  Indeed, China wants to seize these assets by overpowering Vietnam while keeping the U.S. on the sidelines to show that it can engage in a string of hostilities without the U.S. and its partners stopping it. Emboldened, China’s confrontations will continue until it supplants American primacy in Asia or it is met by a resolute balancing bloc.

The U.S. and its Asian partners must meet China’s aggression together.

First, China must realize that escalation is costly. The U.S. should declare that if China continues using force, it will dispatch naval and aerial support near the rig to restore peace and consider sanctioning the subject Chinese energy company and its leaders.

By maintaining ships near the rig and returning water cannon fire, Vietnam has shown that it will stand up to China. Still, Vietnam, which has no defense treaty with the U.S., must calibrate its use of defensive force because it cannot beat China in a maritime battle and it benefits from China being seen as the sole aggressor. Hanoi should thus continue talks with Beijing to reach a nonviolent resolution, but it must not unilaterally withdrawal from the area as Beijing demands. During the Scarborough Shoal incident, the U.S. brokered a deal requiring China and the Philippines to simultaneously remove their ships from the disputed waters, but only the Philippines did so and China has since controlled the shoal. Additionally, Vietnam should continue mobilizing international support and shaming China, because Beijing values its image. Indeed, after the Philippines initiated international arbitration of the Scarborough Shoal incident, China allegedly offered to withdrawal from the area if the Philippines delayed the arbitration.

Other Asian countries clashing with China over territorial and maritime claims should condemn it and announce that Chinese hostility drives them closer to each other and the U.S.  This dynamic is already underway. The Philippines recently increased U.S. access to its military bases and agreed to enhance naval cooperation with Vietnam. Japan announced this week that it would provide maritime aid to Vietnam. India has offered Vietnam a credit line to purchase weapons and agreed to train Vietnam in submarine warfare. The goal is for regional partners to respond jointly when China targets one of them.

Second, Vietnam’s defensive capabilities, including its maritime law enforcement and surveillance capacities, must be strengthened. Additional weapons sales and aid from the U.S., Japan, and India are necessary. The U.S. must therefore revisit its ban on the sale of lethal weapons to Vietnam. To supplement its defense budget, Hanoi can offer these countries’ companies favorable terms to exploit natural resources near its coast. Further, the U.S., Vietnam, and other countries sparring with China should conduct multilateral military exercises.

Third, Hanoi should invite Washington to return to Vietnamese military bases. Given political sensitivities, Vietnam can retain control of its facilities, but grant American forces rotational access and allow them to build new infrastructure and pre-position equipment. America will be able to project power into the South China Sea more easily and China will be deterred from harassing Vietnam.

Fourth, the U.S. should conclude the Trans-Pacific Partnership (TPP). That free trade agreement is being negotiated by the U.S., Vietnam, Japan, and nine other countries that make up over one third of world trade and about forty percent of global output. The TPP will open up its signatories to more trade and investment. For instance, numerous textile companies are moving from China to Vietnam because wages are lower and the TPP will cut textile tariffs. As TPP countries prosper, they can increase their military spending. And by creating such a large market, the pact will reduce its members’ economic reliance on China, giving them greater freedom to oppose Beijing’s power grabs.

The single time that the U.S. and its allies responded firmly to recent Chinese aggression, China essentially backed down. Days after China expanded its ADIZ, Washington, Tokyo, and Seoul sent warplanes through it. The U.S. and Japan provided military aid to Southeast Asian countries embroiled in territorial disputes with China, and Japan increased its military budget and drafted its first national security strategy, which focused on countering China. South Korea enlarged its ADIZ to include areas claimed by China. Beijing has since largely fallen silent about its ADIZ and not followed up on its statements about creating an ADIZ in the South China Sea.

The U.S. and its Asian partners must demonstrate that they can regularly make tough, coordinated responses to Chinese aggression. Otherwise, Beijing will further doubt U.S. commitments and continue trying to control Asia.

Paul J. Leaf is an attorney at an international law firm, a commentator on U.S. foreign policy, and a former editor of the Stanford Law Review.