U.S. officials have long agreed with Mao Zedong’s famous formulation about relations between China and North Korea: the two countries are like “lips and teeth.” Pyongyang depends heavily on Beijing for energy, food, and most of its meager trade with the outside world, and so successive U.S. administrations have tried to enlist the Chinese in their attempts to denuclearize North Korea. U.S. President Donald Trump has bought into this logic, alternately pleading for Chinese help and threatening action if China does not do more. In the same vein, policymakers have assumed that if North Korea collapsed or became embroiled in a war with the United States, China would try to support its cherished client from afar, and potentially even deploy troops along the border to prevent a refugee crisis from spilling over into China.

But this thinking is dangerously out of date. Over the last two decades, Chinese relations with North Korea have deteriorated drastically behind the scenes, as China has tired of North Korea’s insolent behavior and reassessed its own interests on the peninsula. Today, China is no longer wedded to North Korea’s survival. In the event of a conflict or the regime’s collapse, Chinese forces would intervene to a degree not previously expected—not to protect Beijing’s supposed ally but to secure its own interests.

In the current cycle of provocation and escalation, understanding where China really stands on North Korea is not some academic exercise. Last July, North Korea successfully tested an intercontinental ballistic missile capable of reaching the United States’ West Coast. And in September, it exploded a hydrogen bomb that was 17 times as powerful as the one dropped on Hiroshima. U.S. rhetoric, meanwhile, has inflamed the situation. Trump has mocked the North Korean leader Kim Jong Un as “Little Rocket Man,” threatened that North Korea “won’t be around much longer,” and announced that “military solutions are now fully in place, locked and loaded.” To back up these threats, the United States has brought its long-range bombers and naval vessels conspicuously close to North Korea.

The real possibility of chaos on the peninsula means that the United States needs to update its thinking about Beijing’s motivations. In the event of an escalation, China will likely attempt to seize control of key terrain, including North Korea’s nuclear sites. The large-scale presence of both American and Chinese troops on the Korean Peninsula would raise the risk of a full-blown war between China and the United States, something neither side wants. But given how weak Beijing’s ties to Pyongyang are, and given China’s own concerns about North Korea’s nuclear program, the two great powers may find surprising common ground. With some forward thinking, the United States could lessen the risk of an accidental conflict and leverage Chinese involvement to reduce the costs and duration of a second Korean war.

UPDATING THE RECORD

As the conventional wisdom has it, China is unwilling to push North Korea to denuclearize on account of its own insecurities. This thinking is based on three assumptions: that China and North Korea are allies, that China fears instability on the peninsula and the refugee problem that may result, and that Beijing needs North Korea to survive as a buffer state between China and South Korea, a key U.S. ally. These assumptions were true 20 years ago, but Beijing’s views have evolved significantly since then.

Xi in Beijing, October 2015 Jason Lee / Reuters

China and North Korea long enjoyed a closeness born of mutual dependency. Just one year after the birth of the People’s Republic of China, Beijing came to the assistance of its fledgling communist neighbor during the Korean War. To prevent future “aggression” against Pyongyang, the two signed a mutual defense pact in 1961. And when the end of the Cold War robbed North Korea of its Soviet benefactor, Beijing stepped in to provide economic and military assistance. But today, China and North Korea can hardly be characterized as friends, let alone allies. Chinese President Xi Jinping has never even met Kim, and according to Chinese scholars with government access or ties to the Chinese Communist Party, he despises the North Korean regime. The rumor in Chinese foreign policy circles is that even the Chinese ambassador in Pyongyang has not met Kim.

Xi has publicly stated that the 1961 treaty will not apply if North Korea provokes a conflict—a standard easily met. In my travels to China over the past decade to discuss the North Korean issue with academics, policymakers, and military officials, no one has ever brought up the treaty or a Chinese obligation to defend North Korea. Instead, my Chinese colleagues tell me about the relationship’s deterioration and Beijing’s efforts to distance itself from Pyongyang, a change that a Global Times public opinion poll suggests enjoys wide support. As the Chinese scholar Zhu Feng has argued in Foreign Affairs, giving up North Korea would be domestically popular and strategically sound.

Understanding where China stands on North Korea is not some academic exercise.

In fact, the bilateral relationship has gotten so bad that officers in the People’s Liberation Army (PLA) have suggested to me in private meetings that Beijing and Pyongyang may not take the same side in the event of a new Korean war. The Chinese military assumes that it would be opposing, not supporting, North Korean troops. China would get involved not to defend Kim’s regime but to shape a post-Kim peninsula to its liking.

These policies have shifted alongside China’s increasing confidence about its capabilities and regional influence. Chinese thinking is no longer dominated by fears of Korean instability and a resulting refugee crisis. The PLA’s contingency planning previously focused on sealing the border or establishing a buffer zone to deal with refugees. Indeed, for decades, that was probably all Chinese forces could hope to achieve. But over the past 20 years, the Chinese military has evolved into a far more sophisticated force by modernizing its equipment and reforming its organizational structure. As a result, China now has the ability to simultaneously manage instability at its borders and conduct major military operations on the peninsula.

If Kim’s regime collapsed, the People’s Armed Police, which has approximately 50,000 personnel in China’s northeastern provinces, would likely be in charge of securing the border and handling the expected influx of North Korean refugees, freeing up the PLA for combat operations further south. China currently has three “group armies” in the Northern Theater Command, one of the PLA’s five theater commands, which borders North Korea. Each of these armies consists of 45,000 to 60,000 troops, plus army aviation and special forces brigades. And if it needed to, China could also pull forces from its Central Theater Command and mobilize the air force more extensively. When China reorganized its military regions into “war zones” in February 2016, it incorporated Shandong Province into its Northern Theater Command, even though it is not contiguous with the rest of the command, most likely because military leaders would require access to the shoreline to deploy forces to North Korea by sea. The last two decades of military modernization and reform, along with China’s geographic advantages, have ensured that the Chinese military would be capable of quickly occupying much of North Korea, before U.S. reinforcements could even deploy to South Korea to prepare for an attack.

Kim waving in Pyongyang, July 2013 Jason Lee / Reuters

In the past, part of what explained China’s attachment to North Korea was the notion that the latter served as a buffer between China and a once hostile capitalist, and later democratic, South Korea. But China’s increased power and clout have all but eliminated that rationale, too. Beijing may have previously been wary of a reunified Korea led by Seoul, but no longer. Some prominent Chinese scholars have begun to advocate abandoning Pyongyang in favor of a better relationship with Seoul. Even Xi has been surprisingly vocal about his support for Korean reunification in the long term, albeit through an incremental peace process. In a July 2014 speech at Seoul National University, Xi stated that “China hopes that both sides of the peninsula will improve their relations and support the eventual realization of an independent and peaceful reunification of the peninsula.”

Still, the Chinese calculus on South Korea has not completely changed. Enthusiasm for reunification peaked between 2013 and 2015, when South Korean President Park Geun-hye prioritized bilateral relations with Beijing. But after a nuclear test in early 2016 by North Korea, Seoul reinforced its alliance with Washington and agreed to deploy THAAD, a ballistic missile defense system, causing consternation among Chinese officials that their charm offensive was not gaining enough traction. China’s chief concern remains the prospect of U.S. forces in a reunified Korea. Although China still supports Korean reunification, it also wants to shape the terms. And its approach will likely depend on the status of its bilateral relationship with South Korea.

WHAT CHINA REALLY WANTS

Given the costs of a war on the Korean Peninsula, U.S. planners have long thought that China would do everything it could to avoid becoming entangled in a major conflagration involving South Korean and U.S. forces. If China did intervene, policymakers assumed that Beijing would limit its role to managing refugees close to the border or supporting the Kim regime from a distance through political, economic, and military aid. Either way, Washington believed that China’s role would not significantly impact U.S. operations.

This is no longer a safe assumption. Instead, Washington must recognize that China will intervene extensively and militarily on the peninsula if the United States seems poised to move its forces north. This is not to say that China will take preemptive action. Beijing will still attempt to keep both sides from leading everyone down the path to war. Moreover, if an ensuing conflict were limited to an exchange of missile and air strikes, China would most likely stay out. But if its attempts to deter the United States from escalating the crisis to a major war failed, Beijing would not hesitate to send considerable Chinese forces into North Korea to ensure its interests were taken into account during and after the war.

China’s likely strategic assertiveness in a Korean war would be driven largely by its concerns about the Kim regime’s nuclear arsenal, an interest that would compel Chinese forces to intervene early to gain control over North Korea’s nuclear facilities. In the words of Shen Zhihua, a Chinese expert on North Korea, “If a Korean nuclear bomb explodes, who’ll be the victim of the nuclear leakage and fallout? That would be China and South Korea. Japan is separated by a sea, and the United States is separated by the Pacific Ocean.”

China is well positioned to deal with the threat. Based on information from the Nuclear Threat Initiative, a U.S. nonprofit, if Chinese forces moved 100 kilometers (about 60 miles) across the border into North Korea, they would control territory containing all of the country’s highest-priority nuclear sites and two-thirds of its highest-priority missile sites. For Chinese leaders, the goal would be to avoid the spread of nuclear contamination, and they would hope that the presence of Chinese troops at these facilities would forestall a number of frightening scenarios: China could prevent accidents at the facilities; deter the United States, South Korea, or Japan from striking them; and block the North Koreans from using or sabotaging their weapons.

Beijing is also concerned that a reunified Korea might inherit the North’s nuclear capabilities. My Chinese interlocutors seemed convinced that South Korea wants nuclear weapons and that the United States supports those ambitions. They fear that if the Kim regime falls, the South Korean military will seize the North’s nuclear sites and material, with or without Washington’s blessing. Although this concern may seem far-fetched, the idea of going nuclear has gained popularity in Seoul. And the main opposition party has called for the United States to redeploy tactical nuclear weapons to the peninsula—an option that the Trump administration has been reluctant to rule out.

Beyond nuclear concerns, China’s stance on North Korea has shifted as part of its more general geopolitical assertiveness under Xi. Unlike his predecessors, Xi is not shy about China’s great-power ambitions. In a three-and-a-half-hour speech he gave in October, he described China as “a strong country” or “a great country” 26 times. That is a far cry from the dictum that one of his predecessors, Deng Xiaoping, preferred: “Hide your strength, bide your time.” Under Xi, China is increasingly playing the role of a major power, and he has pushed for military reforms to ensure that the PLA can fight and win future wars.

China is no longer wedded to North Korea’s survival.

Most important, a war on the Korean Peninsula would represent a litmus test of China’s regional competition with the United States. Indeed, Chinese concerns about Washington’s future influence best explain why China is unwilling to push North Korea to the degree that the Trump administration wants. China will not risk instability or war if the outcome could be a larger U.S. role in the region. Given this, China no longer feels comfortable sitting on the sidelines. As one PLA officer asked me, “Why should the United States be there but not us?” For this reason alone, Chinese scholars and military leaders argue, China will need to be involved in any contingency on the peninsula.

North Korean soldiers patrolling the banks of the Yalu River, April 2013 jacky CHEN / REUTERS

WORKING TOGETHER

The bottom line, then, is that Washington should assume that any Korean conflict involving large-scale U.S. military operations will trigger a significant Chinese military intervention. That does not mean that the United States should try to deter China: such a response would almost certainly fail, and it would increase the chances of a direct military confrontation between Chinese and U.S. forces. Moves that could damage the relationship between Beijing and Washington would also impede contingency planning or coordination before and during a crisis, raising the risks of miscalculation.

Instead, Washington must recognize that some forms of Chinese intervention would actually be beneficial to its interests, especially with regard to nonproliferation. First and foremost, U.S. officials should note that Chinese forces are likely to make it to North Korea’s nuclear sites long before U.S. forces, thanks to advantages in geography, force posture, manpower, and access to early warning indicators. That is a good thing, since it would reduce the likelihood that the collapsing regime in Pyongyang would use nuclear weapons against the United States or its allies. China could also prove helpful by identifying nuclear sites (with the assistance of U.S. intelligence), then securing and accounting for the nuclear material at those sites, and finally inviting international experts in to dismantle the weapons. The United States, meanwhile, could lead multilateral efforts to intercept North Korean nuclear materials at sea, in the air, or traveling overland and to guarantee their accounting, safe storage, and disposal.

More than anything, U.S. policymakers must shift their mindset to view China’s involvement as an opportunity instead of as a constraint on U.S. operations. For example, the U.S. Army and the Marines must accept that although securing nuclear facilities is currently a key mission in North Korea in the event of a conflict, they will have to change their plans if the Chinese get there first.

At the political level, Washington must be willing to take greater risks to improve coordination with China in peacetime. This may mean bilateral consultation with Beijing, even though that would conflict with Seoul’s preference to keep China at arm’s length. Granted, sharing intelligence with China and jointly planning and training for contingencies would seem unnatural, since the United States is simultaneously engaged in a long-term strategic competition with China. The U.S. Defense Department considers China to be one of its top five global threats, along with Iran, North Korea, Russia, and extremist organizations. But strategic challenges and severe threats often bring together potential adversaries, and rightfully so. With North Korea out of the way, the United States would have more resources at its disposal to address other threats.

Of course, such an effort to cooperate would require a massive degree of coordination. China has long opposed engaging in discussions with the United States on how it would behave in the event of a conflict on the Korean Peninsula or the North Korean regime’s collapse because of its distrust of U.S. intentions and fears that Washington would use those conversations to sabotage Beijing’s attempts to resolve the nuclear crisis peacefully. But China appears to be softening its position. In a September op-ed in the East Asia Forum, Jia Qingguo, a professor at Peking University, argued that China should cooperate with the United States and South Korea, especially on the question of North Korea’s nuclear weapons arsenal. In Jia’s words, “The omens of war on the Korean peninsula loom larger by the day. When war becomes a real possibility, China must be prepared. And, with this in mind, China must be more willing to consider talks with concerned countries on contingency plans.”

If Beijing continues to resist proposals to work together, Washington should consider unilaterally communicating aspects of U.S. contingency plans to reduce the risk of accidental clashes. It could even provide the Chinese side with intelligence to help the PLA secure the most important nuclear facilities. Alternatively, the two countries could use established mechanisms for nuclear security cooperation in the civilian sector, such as the jointly established Center of Excellence on Nuclear Security, or organizations such as the International Atomic Energy Agency to conduct technical training. No country has more experience dismantling and securing nuclear weapons than the United States. Although China has the manpower to seize control of the sites, it is unclear whether it has the expertise necessary to render safe, transport, or destroy nuclear weapons and material. Sharing best practices would help ensure that China can safely handle what it will find at these sites.

Every strategy has its tradeoffs. Coordinating with or conceding to Chinese involvement in a Korean contingency does have a number of downsides, as critics are bound to point out. For starters, the South Koreans completely oppose the idea of any Chinese involvement on the peninsula, let alone Chinese boots on the ground. U.S. moves to coordinate efforts with China would harm U.S. relations with Seoul, although the benefit of managing the demise of North Korea at a lower cost would be worth it.

Potentially more worrisome is the fact that Chinese intervention in North Korea would entail the loss of some U.S. influence on the peninsula. At a fundamental level, China would be acting not to assist the United States but to ensure that a reunified Korea would not include U.S. troops. But that may not be so bad, after all. In frank discussions, Chinese interlocutors have insinuated that Beijing may yet accede to a U.S. alliance with a reunified Korea. In that case, the end of a permanent U.S. military presence on the peninsula would be a reasonable price to pay to ensure that a second Korean war had the best possible outcome.