As President Donald Trump trades threats with North Korea, China is staying idle. Through assertive military exercises and statements, Beijing has warned repeatedly that it could defend North Korea if it is attacked by the United States. Yet at the same time, a series of shifts in China’s military posture near the North Korean border suggest a military increasingly willing to send forceful signals to Kim Jong Un: At times of heightened tensions, the Chinese military appears to be preparing itself for the fall of Pyongyang. Though America cannot know precisely when and how it would intervene, this much is certain: China is prepared to keep the peace on the Korean peninsula—whether the White House likes it or not.As China says tensions with North Korea are “now at a tipping point approaching a crisis” following its firing of a ballistic missile over Japan, a close look at Beijing’s military signaling reveals that it is quietly working to sharpen the U.S. choice on North Korea. If Trump opts for a military option, he could find himself not only in a damaging war with North Korea but also, potentially, with China. On the other hand, if the United States can set aside his unrealistic military options, China may help to deter the Kim regime from exploiting its new long-range missiles to act aggressively in the region or escalating a crisis already out of control. If China will not help America eliminate North Korea’s nuclear arsenal, it may help it to keep it from being used.

Beijing’s primary concern with respect to the Korean peninsula remains the stability of the region. If Pyongyang collapsed, refugees and armed North Korean soldiers, fissile material, or even nuclear fallout, could stream over the Yalu and Tumen rivers, which form the border with northeast China, presenting a major challenge to its own stability. To prevent this, China has historically acted to ensure that the regime in Pyongyang remains economically viable and that the United States and its allies do not attack. Some in Beijing still see North Korea as a buffer against American power: if U.S. forces invaded, the result could be a peninsula unified under a pro-American liberal democracy, with U.S. troops stationed on China’s border. Over the years, these concerns have caused China to back North Korea against American threats. However, in recent years, there have been an increasing number of voices in Beijing who see North Korea less as a pillar for regional stability and more as a threat to it.In recent years, China’s military has begun preparations for instability with North Korea, starting at the border. Since at least 2013, Chinese military units in the Jilin and Liaoning provinces that border North Korea have received considerable resources. A new border-defense brigade has conducted publicized drills and exercises, reinforcing the existing border guards. A 24-hour video surveillance system and drones watch the river for signs of intrusion. If an economic crisis in North Korea sent refugees to the Chinese border, these units would attempt to seal it.

These steps send strong signals to both Pyongyang and Washington. For years, China has resisted American overtures to discuss and jointly plan for collapse scenarios, a stance that, in effect, supported the Kim regime. By remaining ambiguous about its intentions, Beijing kept Washington from applying maximum pressure to Pyongyang or planning for a conflict. It’s not difficult to imagine U.S. and Chinese forces coming into contact as both race to secure North Korea’s nuclear facilities, leading to a wider conflict. Border fortifications are a sign that the debate in Beijing is evolving to recognize that North Korea is a source of instability and therefore a threat.China took another major step towards addressing the North Korean menace in August when General Joseph F. Dunford, the highest-ranking U.S. military official, visited China and was shown live fire drills at its northern theater command in Shenyang, not far from the North Korean border. Dunford also reported that he had discussed a North Korea “contingency” with China, and the two sides signed an agreement to improve communication between the militaries. Though any coordination would surely be slow to develop, from Pyongyang, this could all look like an ominous sign of an emerging united front.

Yet China is not just defending its border; it is also preparing to fight inside North Korean territory. China’s drills in its Northern district involve not only border-defense forces, but also expeditionary forces—including mobile brigades equipped with some of China’s most advanced military equipment, airborne units, and special-operations forces. At periods of heightened tension in August 2015 and April 2017, there were credible rumors that China moved significant concentrations of forces to its border. In April, U.S. military officials told CNN that China alerted its bomber forces. In July and August, China’s navy repeatedly staged live-fire exercises across the Yellow Sea from the Korean peninsula, practicing engaging targets above, on, and beneath the surface of the sea, as well as ones on land. China customarily denies all such alerts and redeployments, making them difficult to confirm, but some are backed by suggestive video evidence from inside the country or confirmed by reputable outlets speaking to U.S. or Chinese defense officials.

But if China were to fight in North Korea, would it be fighting with the regime or against it? A recent editorial in China’s Global Times reiterated the terms of the 1979 China-DPRK alliance commitment: if the United States were to strike North Korea first, China should defend it; but if North Korea strikes against Guam or otherwise precipitates a conflict, China should remain neutral. In other words, if North Korea starts a war, they’re on their own.

Yet, declining relations between the countries and China’s military posturing raise the possibility that it could enter a war fighting against North Korea. At an internal meeting in May, a North Korean official reportedly told a group of state officials that the country’s missiles could reach all of China. Such threats have some in Beijing quietly concerned that North Korea could pose a direct threat to their country. In a crisis, Kim Jong Un could attempt to force China’s hand, or perceive its defensive operations as an invasion. Either could lead to North Korean missiles deliberately falling on Chinese territory. Around Shenyang, it is not only fences and outposts that are going up but also hardened bunkers capable of shielding against nuclear or chemical attacks.China’s enhanced military posture is meant to convey one simple message: If war breaks out on the peninsula, it won’t be Donald Trump or Kim Jong Un shaping the terms of the conflict, but Beijing. China has not been and in all likelihood will never be willing to endanger the economic viability of the North Korean regime, because doing so would imperil its own security. Beijing has calculated that it cannot force the regime in Pyongyang to disarm, but what it can do is try to deter the use of those weapons.

The United States and its allies can never depend on China for their defense. As long as North Korea remains a nuclear state, it will be necessary to maintain and even strengthen the U.S. presence on the peninsula, to deter North Korea and to resist China’s attempts to eject American forces from the region. Yet the United States and China share an interest in regional stability—stopping North Korea from starting a war. China’s recent military moves suggest it is willing to threaten force to keep the peace. If U.S. officials explored the issue, they might find Chinese military officers willing to deconflict military operations, to coordinate deterrent threats and military operations with their U.S. counterparts, or even to finally open the crucial dialogue on planning for a North Korean collapse. When Kim Jong Un looks out from Pyongyang in coming years, he may find himself without an ally to hide behind, and think twice about acting aggressively.

Coordinated deterrence is only possible if Beijing sees Washington as dedicated to stability. The Trump administration will have to abandon its quixotic theory that it can create a crisis so intense that North Korea will fall to its knees and volunteer to abandon its nuclear weapons. Instead, the United States must follow the path that Seoul, Tokyo, and now Beijing have laid out: to contain and deter the regime in Pyongyang and preserve a stable Northeast Asia.

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