The Singapore summit is the result of a two-step diplomatic process in which South Korea and North Korea, and then the United States and North Korea, gambled on diplomacy. But lurking behind these twin maneuvers is China, an absent but crucial player in the fast-moving diplomacy of the past year.

The only place Kim Jong-un has traveled outside of the Korean Peninsula in the last seven years is to China. Twice this spring, Kim was there to meet with President Xi Jinping. Shortly after the second visit, in May, North Korean media released statements condemning South Korean military drills and threatening to walk away from the Trump-Kim summit. Those statements specifically named high-level members of Trump's government, calling National Security Adviser John Bolton "repugnant” and Vice President Mike Pence a “political dummy.” (This was perhaps because both American officials had publicly advocated a so-called Libya model of instant denuclearization, which North Korea has explicitly rejected.) But U.S. President Donald Trump had his theory for Pyongyang's shift in tone, one that did not involve anyone in his administration. Trump suspected that Xi Jinping had emboldened Kim and that he had done it during that second visit to China. "There was a difference when Kim Jong-un left China the second time," Trump said. “I’m just saying, maybe nothing happened and maybe it did.”

North Korean diplomacy has been marked by this kind of paranoia on all sides; from Xi, that Kim was getting too close to the U.S. and South Korea; then from Trump, that Xi was turning Kim against him; and most of all, from South Korea's Moon Jae-in, that both his country and his lifelong peace project were in danger. Part of the suspicion surrounding China, in particular, stems from haziness about Xi's motivations and his government's ever-changing relationship with North Korea.

Since the beginning of 2018, when, in his New Years' Day address, Kim signaled for the first time that he was open to diplomacy, two central interpretations of China's influence on North Korea have emerged. The first is that China has been sidelined. This theory was most widespread early in the year, as Trump accepted an invitation to a bilateral U.S.-North Korea summit, and Moon and Kim signed a Panmunjom declaration that largely left out China. The second view, which Trump endorses, is the opposite: that China can control North Korea—and is therefore responsible for its actions. Trump attributed intensified rhetoric from Pyongyang to Xi's influence and scolded China on Twitter for not being “strong and tight” enough in its enforcement of the newly “porous” border with North Korea. Also, Trump has previously claimed in 2013, that “China could solve this problem easily if they wanted to but they have no respect for our leaders.” Likewise, Trump has given some credit to China when North Korean diplomacy has gone well. For instance, in his announcement that the summit was back on, Trump thanked Xi, saying he “helped me quite a bit on this.”

Neither extreme interpretation is correct. China cannot manipulate North Korea as its vassal state, nor has it been pushed into irrelevance. Instead, North Korea relies on China economically but is not entirely beholden to it. China hopes to influence North Korea as a means of strategically competing in Asia but is on alert that the U.S. will attempt to do the same.

For the best chance of success during and after the summit, the Trump administration must reassess China’s power with the hermit kingdom. That requires identifying Chinese interests and knowing where they diverge from American ones. On some issues, like ensuring stability on the Korean peninsula, Chinese and American priorities are aligned, up to a point. Should instability rear its head, Washington might push for regime change, whereas Beijing would almost surely prefer the status quo. On other issues, like limiting U.S. military presence in Asia, they are directly opposed. China’s near-irrational opposition to the deployment of a single U.S.-owned Theater High Altitude Area Defense (THAAD) system, in 2016, revealed its resistance to any augmentation of America’s defense posture on the peninsula. And on the issue of denuclearization, the U.S. and China also disagree. The U.S. expects a commitment to complete, verifiable, and irreversible denuclearization (CVID)—although not immediate, as a “Libya” model would entail—but China supports a ten-year, or phased, approach, which North Korea also favors. These differences do not necessarily prevent a breakthrough with North Korea that benefits both the U.S. and China, but failure to account for them before the negotiations begin would leave the U.S. at a strategic disadvantage.

Trump's belief that China has an enormous influence on North Korea did not come from anywhere. If North Korea has anything resembling an ally in the world, it is China. For one thing, China is North Korea's economic lifeline, providing up to ninety percent of its foreign trade. And for another, the two countries share an 880-mile-border and a seventy-year history. In 1950, defying the expectations of the American military, a fledgling People's Republic of China came to the defense of its communist neighbor against U.S. and U.N. forces at a high cost. The result was that the war killed as many as 400,000 Chinese military members. That friendship between North Korea and China lasted through the Cold War, into the next millennium. In 2002, when President George W. Bush named North Korea, along with Iran and Iraq, an "axis of evil," the Chinese pushed back on language that might have been seen as a pretext for regime change. "The Chinese side does not advocate using this kind of language in international relations," a Chinese foreign ministry spokesman said at the time. Furthermore, in 2003, Beijing hosted the first Six Party Talks in an attempt to denuclearize North Korea. Throughout those talks—until a September 2005 pledge to eliminate nuclear weapons evaporated in 2006 when Kim’s father conducted his first nuclear test—then-Chinese President Hu Jintao played a crucial mediator role.

But North Korea’s relationship with China is also fraught and has grown that way since 2011 when Kim Jong-un came to power. More nuclear tests and fewer diplomatic visits, combined with provocations like the assassination of Kim’s pro-China uncle in 2013, have unnerved Beijing. Tensions only increased in the fall of 2017, when China joined in on U.N. sanctions, providing the economic squeeze required to make the Trump administration’s “maximum pressure” strategy effective. At this record moment of estrangement between the two countries, Mao Zedong’s aphorism, that China and North Korea are as close as “lips and teeth,” is long outdated. Kim’s 2018 decision reduce tensions with South Korea and the United States thrust North Korea and China back into a marriage of convenience. Thus, the U.S. would be equally misguided to underestimate China’s influence—and desire for influence—with North Korea. This is especially true under the leadership of Xi, who is not only poised to be president-for-life but has asserted that his country will “take center stage in the world.” In other words, Xi’s China will never be sidelined.

In the North Korean negotiations, Xi sees an opportunity both to be viewed as an international mediator and to advance China’s position in strategic competition with the U.S. As Jeffrey Wasserstrom has noted, Xi's philosophy or "thought," inserted into the constitution last year, has one overarching message: "China is poised to regain its stature as a great country." A significant threat to that goal would be a reunified peninsula on which the U.S. has substantial influence, via its ally South Korea, while China remains alienated from North Korea. But China's fears about the closeness between the U.S. and the Koreas were likely eased when Trump sent a letter to Kim canceling the June 12 summit. Though Trump re-committed to the summit eight days later, the move isolated both the South Koreans, who were not notified ahead of time, and the North Koreans, whom Trump momentarily rejected. China, by contrast, has recently enjoyed a closer relationship with South Korea, after beginning to normalize relations last fall following a period of tension related to American military cooperation. Also, China has warmed again to North Korea since Xi's meetings with Kim. Indeed, news reports indicate that China has begun easing economic sanctions, or at least the enforcement of them, as the summit approaches, and is unlikely to sacrifice that improved relationship if the U.S. seeks their help to apply pressure once again.

Finally, as much as Trump and Xi compete for influence with North Korea, it is crucial not to underestimate Kim as a strategist on his own terms. Kim has two fundamental goals: recognition as a nuclear power and the economic development of his country. He has already made progress on both fronts. The first goal, recognition, will come from a photo-op with an American president in Singapore and from the meetings he has already had, with Moon and Xi. The second goal, economic advancement, will come primarily with sanctions relief and, potentially, from development. For example, in the lead-up to the summit, China not only relaxed economic pressure, but appears poised for major investment in North Korea if Trump and Kim establish a new rapprochement.