Chinese naval officers wait dockside as a Chinese naval warship escorting the USS Curtis Wilbur arrives on Sept. 13, 2005, in Qingdao, in Shandong province. (Frederic J. Brown/AFP/Getty Images)

On March 31, Taiwan’s Ministry of Foreign Affairs reported that two Chinese Air Force (PLAAF) J-11 jets crossed the median line of the Taiwan Strait. This violated the long-held tacit agreement between China and Taiwan that neither side should cross the median line.

Taiwan deemed this “an intentional, reckless & provocative action,” which triggered “a 10-minute standoff” in the air. As Asia security expert Bonnie S. Glaser notes that, if intentional, this would be the first PLAAF crossing of the median line in about 20 years. In this case, it’s likely that Taiwan, not the South China Sea, prompted Beijing’s actions.

An unresolved issue from the Chinese civil war, Taiwan has always been a “core interest” to party leaders in Beijing. Here are some key takeaways from my research on China-Taiwan relations.

What does the PLAAF move signal?

Granted, there is much we don’t know about this specific PLAAF incident. But my work on cross-Strait relations suggests that it’s quite possible the PLAAF behavior is intentional — and serves as a coercive signal to Taiwan and the United States. Here’s what you need to know:

1. The U.S. agreed to sell fighter jets to Taiwan.

In March, the United States agreed to sell F-16V fighter jets to Taiwan — the fourth-generation model. The last U.S. sale of F-16s to Taiwan took place in September 1992.

Beijing considers selling weapons platforms such as jet fighters and submarines to Taiwan an implicit red line. In the past, China used coercion to deter countries from selling these weapons platforms to Taiwan. This suggests that last week’s PLAAF incident is intended to send a deterrent signal about fighter sales to both Taiwan and the United States.

The Chinese Foreign Ministry and Ministry of Defense lodged protests against the United States regarding the sale, reiterating that China will “take all necessary measures” to resolutely defend its sovereignty. The Trump administration decided on April 5 to put on hold the F-16V deal until the United States strikes a trade deal with China, suggesting that China may have used the bilateral trade talks as a bargaining chip.

2. U.S. ships were in the Taiwan Strait.

On March 24, U.S. naval and Coast Guard ships passed through the Taiwan Strait. The Chinese Foreign Ministry protested, urging the United States to exercise caution.

3. Taiwan’s president stopped off in Hawaii.

That same week, Tsai Ing-wen made a U.S. stopover. China protested that this was in violation of the “one China” policy, which calls for the United States and other countries to refrain from official diplomatic relations with Taiwan.

These actions appear to be relatively minor provocations in China’s ledger. But to Beijing, not taking coercive actions to demonstrate its resolve might produce more provocative actions from Taiwan and the United States in the future.

How does China use its tools of coercion?

In the past, China has utilized both military and nonmilitary tools to force Taiwan and other countries to stop and deter actions that China deems threatening. My book project suggests that China uses these tools selectively. And Beijing tends to target the United States less, because of China’s economic vulnerability vis-a-vis the United States.

Here’s an example. When France sold Mirage 2000 fighter jets Taiwan in 1992, China responded with harsh diplomatic and economic sanctions, including a ban on French wheat exports to China, awarding a subway bid in China’s southern city of Guangzhou to Germany, freezing a French project to build a nuclear power plant in China and closing the French consulate in Guangzhou.

In this case, China had “exit options.” For instance, France, Germany and the United Kingdom were all bidding on the Guangzhou subway project. The Chinese ambassador to France stated in his memoir that China turned to Germany to sanction France.

Fear of U.S. economic retaliation held China back in 1992.

Concerns about U.S.-China economic relations kept Beijing from giving a similar response after the 1992 U.S. sale of F-16s to Taiwan. Just 12 days after the sale, Congress passed a bill linking Most Favored Nation (MFN) trade status with Chinese human rights conditions.

Evidence from my working paper reveals that Chinese government analysts during the 1992 F-16 episode waited anxiously. Would President George H.W. Bush veto the conditional extension of MFN status — and would Congress then overturn the veto? Bush eventually vetoed the bill, 26 days after the sale.

Losing MFN status would be detrimental to China’s exports, a former World Bank official in charge of China confirmed to me. And China and the United States were slated to engage in market entry negotiations three weeks after the weapons sales. The U.S. trade representative threatened 100 percent tariffs on $4 billion worth of Chinese goods if the two sides did not reach an agreement.

China expert John W. Garver writes that Deng Xiaoping endorsed an internal Chinese Foreign Ministry report at the time, because “China needed to give priority to economic interests” and avoid a trade war in which Beijing stood to lose the most.

By 1994, President Clinton had delinked MFN status from Chinese human rights conditions. China subsequently responded with coercion in 1995 when Taiwanese President Lee Teng-hui gave a talk at Cornell University and Taiwan held elections in 1996. Beijing conducted missile tests and recalled the Chinese ambassador to the United States.

These measures, Beijing hoped, would deter the United States and other countries from granting Lee a visa in the future, which China perceived as supporting Taiwan’s path toward de jure independence.

In this light, President Tsai Ing-wen’s recent transit via Hawaii and meetings with senior U.S. leaders could be a contributing factor to China’s reactions. Barring an official invitation for the Taiwanese president to visit the United States, Chinese coercion regarding these transits probably will focus on Taiwan. China’s goal, most likely, is to deter Taiwanese leaders from transiting via the United States or meeting with senior U.S. officials in the future.

China and Taiwan have long had a tense relationship. But as Chinese economic clout increased, Beijing began to threaten economic and diplomatic sanctions against U.S. weapons sales to Taiwan. In the long run, if China successfully diversifies its export markets and becomes less dependent on U.S.-China trade, Beijing is likely to become more coercive — especially regarding Taiwan.

Ketian Vivian Zhang is a postdoctoral fellow at the Shorenstein Asia-Pacific Research Center at Stanford University. She will join the Schar School of Policy and Government at George Mason University in summer 2019 as an assistant professor of international security.