Naturally, everyone assumes that Kim Jong-Un’s aggression targets the United States. What we have missed is that the other real target of Kim’s aggression is China.

Less than two weeks ago, U.S. Secretary of State Rex Tillerson praised Kim Jong-Un for having “demonstrated some level of restraint that we’ve not seen in the past.” As if determined to prove Tillerson wrong, Pyongyang first fired an intercontinental ballistic missile over Japan. Then on Sunday, September 3, Kim gave the order to detonate what he claimed to be a hydrogen bomb (H-bomb) that could be attached to a missile capable of reaching the mainland United States.

Whether North Korea successfully tested an H-bomb is yet to be verified. But early indicators show the nuclear device that Pyongyang tested was much more powerful than anything it tested before. Chinese media reported that the test “triggered a 6.3-magnitude quake followed by a 4.6-magnitude tremor, and was felt throughout northeastern China.”

Sunday’s was North Korea’s sixth nuclear test, but the first since Trump became president. Naturally, everyone assumes that Kim Jong-Un’s aggression targets the United States, so everyone is asking what the U.S. response should be. What we have missed is that the other real target of Kim’s aggression is China.

How China Fueled North Korea’s Nuclearization

After each North Korean missile and nuclear weapon test, China always condemns Pyongyang and states all nations should work towards denuclearizing the Korean peninsula. Yet if not for China, Pyongyang probably wouldn’t have made such speedy progress in its nuclear weapon development.

On October 16, 1964, China successfully tested its first nuclear weapon, a 16-kiloton bomb, at a site in Inner Mongolia. It came as a shock to the United States because U.S. intelligence initially doubted China had enough weapons-grade uranium to make a nuclear bomb. Even after China’s successful test, the U.S. military arrogantly declared that “the acquisition by Communist China of nuclear weapons will not, for the indefinite future, alter the real relations of power among the major states, or the balance of military power in Asia.” History has proved they couldn’t have been more wrong.

The political situation in Southeast Asia soon got complicated. China and India’s relationship went sour after two border wars in 1962 and 1967. After India successfully tested its first nuclear device in 1972, China’s leader, Mao Zedong, decided to prop up Pakistan’s military capacity to create a counterweight to India. Mao and Pakistani President Zulfiqar Ali Bhutto reached an agreement in 1976, stating that China would provide support to Pakistan’s nuclear weapon development.

In his book, “The Beautiful Country and the Middle Kingdom,” John Pomfret, a long time Asia correspondent to The Washington Post, wrote that “In 1982, Deng Xiaoping authorized the transfer to Pakistan of a blue-print for one of China’s early nuclear bombs along with 110 pounds of weapons-grade uranium, enough for two nuclear devices.” China proliferated nuclear weapons technology to Pakistan throughout the 1980s and 1990s, and such action has led to grave consequences. A group led by Pakistani nuclear scientist A.Q. Khan sold China’s blueprint to Libya, Iran, and North Korea. As they say, the rest is history.

China’s nuclear proliferation to Pakistan supplied North Korea the nuclear technology it needed. Meanwhile, Chinese trade and aid helped sustain North Korea economically and provided Pyongyang the means to become a nuclear power. Thus, China can’t claim it’s an innocent bystander of North Korea’s nuclearization today. Yet, despite China’s support, North Korea had little appreciation for China’s patronage.

Soured Sino-North Korea Relations

Once upon a time, China and North Korea were really close. Chairman Mao described the two communist regimes’ relations as close as “lips and teeth.” At least 180,000 Chinese soldiers gave their lives during the Korean War. After Chinese leader Mao’s passing, the two countries began to slowly drift apart. China opened its door to the rest of the world. It embraced “market reform with socialist characteristics” and dramatically improved its economy and standards of living.

North Korea turned inward, becoming a dynastic totalitarian regime. It devoted all its limited resources to sustaining generations of the Kim family’s luxurious lifestyle and military buildup, while its people continue to live in poverty and misery.

After North Korea tested a nuclear weapon in October 2006, China supported a United Nations Security Council Resolution to impose sanctions on North Korea, after maneuvering to water the sanctions down. This marked the first sign of a strained Sino-North Korea relationship. China further irritated North Korea by increasing its trades with South Korea. Even though the bilateral trade volumes between China and North Korea continue to increase and China doesn’t always either support or fully implement international sanctions against North Korea, North Korea still feels a sense of betrayal.

The relationship really went downhill after Kim Jong-Un took over. Kim openly ignored China’s warnings and aggressively pursued nuclear weapon development. In the process of consolidating power, he killed North Korean elites who used to work closely with China, including his own uncle and half-brother. North Korean official media also made several rare but open criticisms of China, warning “China had better ponder over the grave consequences to be entailed by its reckless act of chopping down the pillar of the DPRK-China relations.”

China has always been quick to point out that the United States is the target of North Korea’s aggression. But if we examine the timing of North Korea’s recent missile tests and the nuclear weapon test, it seems Pyongyang has acted defiantly to China too. For instance, Kim Jong-Un ordered missile tests when Chinese President Xi and U.S. President Trump met in April. He did it again in May when China was hosting its “One Belt One Road” summit.

The latest H-bomb test took place when the BRICS countries—Brazil, Russia, India, China and South Africa—were convening in China for their annual summit. So each time China was playing its role as a benevolent rising power and hosting an important event, North Korea did something to ruin the party and steal China’s thunder.

It’s an open secret that China has little love for North Korea. Chinese leaders haven’t invited Kim Jong-Un to visit Beijing so far. China keeps supporting North Korea because “it dislikes even more the prospect of North Korea’s collapse and the unification of the Korean Peninsula with Seoul as the capital,” writes Richard N. Haass. Thus Chinese leaders continue to view North Korea as a necessary evil to serve as a buffer between China and the United States and its ally.

That kind of old-school, Cold War mentality is now being challenged inside China. The Chinese public has a very negative opinion of the North Korean regime. Just like Americans, the majority of Chinese view Kim as a crazy guy and the North Korean regime as a security threat to China. In recent years, Chinese elites, sensing the shifting attitudes from the public as well as the party leadership, began to openly advocate for China either “not be a saviour if the North Korean regime collapsed or started a war” or “ abandon Pyongyang and support the unification of the Korean peninsula.”

China Needs to Step up for Its Own Security

There’s a Chinese saying, yang hu wei huan (養虎為患): “nurturing a tiger invites calamity,” which means indulging one’s enemy is asking for trouble. This is the situation China is in right now. North Korea is a tiger China indulged and now threatens to bite the hands that fed it.

Chinese President Xi desperately needs stability domestically and along China’s border in preparation for the upcoming leadership reshuffling at the 19th Communist Party Congress, which takes place in October. But Kim Jong-Un won’t let Xi have it.

It should be obvious to China now that North Korea is no longer the security buffer China seeks, but rather a time bomb that will explode and drag China down with it.

The latest nuclear weapon test created several headaches for Xi. One is the concern of possible nuclear contamination of China’s northeast region, which shares a border with North Korea. Since environmental pollution has been the number one cause for street protests and social unrest in China, Chinese state-backed Global Times declared that if China confirms that Pyongyang’s nuclear test contaminated Chinese soil, “the current framework for Sino-North Korean ties will break down,” and “the conflict between China and North Korea will transcend any conflict between the US and North Korea.”

Another concern China has is that Japan is making more and more noise to acquire nuclear weapons in response to the North Korean buildup. Given the historical animosity between China and Japan, the last thing China wants to see is a nuclearization of Japan. It should be obvious to China now that North Korea is no longer the security buffer China seeks, but rather a time bomb that will explode and drag China down with it.

International crises sometimes makes strange bedfellows. The United States and former Soviet Union joined forces to fight the Nazis. China and the United States became allies against the former Soviet Union’s aggression. Recognizing that North Korea threatens the security of both China and the United States should change the strategic calculations and approaches of both nations.

The time is ripe for China to ditch past pretense and a Cold War mentality, instead becoming an active and honest partner with the United States to address a problem that China helped create. Neither China nor the United States has any good options to deal with North Korea on its own, but by working together, and only by working together, the two countries can come up with the most effective solution with the minimum costs to them and to the rest of the region.