Amidst rising tensions in Northeast Asia, U.S. Secretary of State Rex Tillerson's upcoming visit to the region this week offers a glimmer of hope that diplomacy could avert a military conflict with North Korea.

For Tillerson, this will be the toughest test of his diplomatic skills. The odds that the secretary of state's trip will cobble together a regional coalition to contain Pyongyang's nuclear and missile ambitions do not appear good. South Korea has plunged into political chaos after the recent impeachment of President Park Geun-hye. Its political elites are deeply split over North Korea, which Tillerson is expected to visit on Friday. Japan, America's staunch ally where Tillerson is expected to make his first stop Wednesday, will likely provide unreserved support. In China, Tillerson will almost certainly find his toughest interlocutors when he visits next weekend.

To Washington, Beijing's response to Pyongyang's brinksmanship has long been a source of frustration. As North Korea's patron, only China has the means to pressure the Kim Jong-un regime to moderate its behavior. To be sure, in recent years Beijing has taken some modest measures trying to rein in Pyongyang. For example, China has supported sanctions against North Korea at the United Nations Security Council. Last month it also announced the suspension of coal imports from North Korea.

However, by and large, the Chinese government has refrained from imposing sanctions that could trigger a collapse of the North Korean economy and the Kim dynasty. In China's strategic calculation, even a nuclear-armed North Korea bristling with missiles is preferable to a unified Korean peninsula allied with the United States.

It is this strategic logic that has led Beijing to adopt a policy that, instead of dialing up pressure on Pyongyang, ratchets up tensions with Washington and Seoul. Specifically, China has been incensed by America's decision to deploy an advanced anti-missile system, known as Terminal High-Altitude Area Defense (Thaad), in South Korea because the Chinese military fears that the system could render China's own nuclear deterrence more vulnerable.

Unable to force the more powerful U.S. to back down, China has concentrated its ire on South Korea. In the last two decades, South Korea has been playing a delicate balancing geopolitical game of relying on the U.S. for security protection and on China for trade. Now this game may be over because China is forcing South Korea to choose. In an effort to show Seoul the costs of hosting Thaad, Beijing has ordered a suspension of the sale of tour packages to South Korea and denied visas to Korean performers. On March 9, in a further escalation, Chinese authorities shut down half of the stores operated by Lotte, one of South Korea's largest conglomerates.

On the surface, China seems to have a strong hand because it is South Korea's largest trading partner. In 2016, Korea exported $124 billion worth of goods to China and ran a surplus of $37 billion. Additionally, 8 million Chinese tourists visited South Korea last year, spending $19 billion. In the eyes of Chinese leaders, sooner or later Seoul will have to capitulate because it cannot afford to lose its lucrative business with Beijing.

South Korea's political upheaval has also created an opening for China. President Park has pursued a get-tough policy toward Kim Jong-un and agreed to the deployment of Thaad. Now that she is gone and the left-leaning opposition advocating a softer line may replace her, China could use its economic leverage to tip public support in favor of the opposition, which Chinese leaders hope to persuade to back out of the Thaad deal with the U.S.

However compelling this logic, China's pressure tactics may not work. Even if the opposition should come to power, its leaders will likely stick with the Thaad agreement. If forced to choose, it is a safe bet that Seoul would pick Washington, not Beijing, for even more compelling security and economic reasons. In terms of security, China simply cannot replace the U.S. as a provider of security because it has not demonstrated its ability or willingness to deter North Korea. Economically, the U.S. remains South Korea's second-largest export market (in 2016, Korean exports to the U.S. were about $70 billion). It is inconceivable that Seoul would risk losing access to the American market if it realigns with Beijing.