The US has approved a potential multibillion-dollar arms sale to Taiwan — the latest signal that the Trump administration is fed up with China’s aggressive foreign policy.

On Monday, the State Department announced that the US could sell $2.2 billion in weapons, including 108 Abrams tanks and around 250 Stinger surface-to-air missiles, to the small island nation and staunch US ally. That paves the way for America to officially deliver those weapons at some point down the line.

But the authorization on its own has added to longstanding tensions between Taiwan and China. They are still considered one country by both governments and by much of the world. But in practice, they have been totally separate since 1949, when China’s Kuomintang (Nationalist Party) leaders fled to the island of Taiwan and started a government there.

Since then, relations between China and Taiwan have been very poor, with periods of low-level conflict and even moments when it looked like there would be a full-blown war.

The US doesn’t officially recognize Taiwan as a sovereign nation — it only recognizes China — but this big-ticket arms sale proposal highlights how Washington has long treated Taiwan as a separate, independent country in everything but name.

Which means the decision could increase the China-Taiwan animosity. The Chinese government has already requested that the US cancel the authorization, while Taiwan’s President Tsai Ing-wen — who noted in March that her country requested the weapons — tweeted her appreciation for the Trump administration’s decision.

Pleased that the #US government has approved another arms sale package, boosting #Taiwan’s self-defense capabilities. We’ll continue to speed up investment in national defense, & partner with like-minded countries to defend democracy while promoting regional peace and stability. pic.twitter.com/dw4Rw58hYb — 蔡英文 Tsai Ing-wen (@iingwen) July 9, 2019

The timing also doesn’t help. The US and China are locked in tense trade negotiations to end a year-long tariff war, and both nations have ramped up patrols in Asian waters, increasing the risk of a maritime confrontation. If there was ever a moment to keep relations calm, some experts say it’s now.

Others are less concerned, though. “It’s important for the US government to sustain its unofficial relationship with Taiwan regardless of the ebbs and flows of relations with Beijing,” Abraham Denmark, a former top Pentagon official focusing on Asia, told me. “We should be able to manage trade tensions or other issues with China while also working with Taiwan.”

It’s a fair point. After all, the 1979 Taiwan Relations Act compels the US to “make available to Taiwan such defense articles and defense services in such quantity as may be necessary to enable Taiwan to maintain a sufficient self-defense capability.” Sending tanks and missiles could help Taiwan protect itself against a long-feared land invasion by China to bring it back under Beijing’s control.

So the weapons sales, on one hand, are really about keeping an ally happy and safe. But on the other hand, they’re also about putting Beijing on notice.

How China might respond to Taiwan arms sales

June Dreyer, an expert on China and Taiwan at the University of Miami, told me the arms sales are part of a broader message the US is sending to Beijing.

“I see this as a natural outgrowth of signals we’ve been sending to the Chinese for some time,” she said. “The US clearly feels that China has gone too far and that it’s time to stop.”

The list of American grievances against China is long. Among other indiscretions, Beijing has stolen US technological and personnel secrets for its own advantage, antagonized US allies in the South China Sea, killed or imprisoned more than a dozen American informants, and taken millions of US jobs over the past two decades.

On top of that, Chinese President Xi Jinping has pushed to give Beijing much more control over the citizenry, including crackdowns on democracy in Hong Kong and forcing more than a million Uighur Muslims into reeducation camps. Those actions, in part, have led to increasing fears that he may want to seize Taiwan.

“The only thing that will make him the greatest leader in the Chinese Communist Party’s history is to take Taiwan back,” Shen Dingli, an international relations scholar at Fudan University in China, told Quartz in 2018.

That’s unlikely to happen solely because of the arms sales, said Dreyer, and also because the US has vowed to defend Taiwan against Chinese aggression. What’s more, Beijing is still dealing with the fallout after big demonstrations in Hong Kong stopped a bill (at least for now) that would’ve given the Chinese central government more control over the city.

But what China could do in response, she noted, is conduct lower-level provocations like holding war games near the island, harass US ships in nearby waters, arrest Taiwanese or US citizens on spying charges, and much, much more. “The retaliation will be carefully calibrated,” she continued, adding that China could respond more forcefully when there’s less attention focused on it.

Which means US-China problems may be relatively subdued now, but they could become a whole lot worse in the months to come.