This essay was originally published in Foreign Affairs magazine.

This is a welcome development for Beijing. Chinese analysts view South Korea as a weak link in the United States’ East Asian alliances, and Beijing is trying to divide Washington and Seoul through a combination of compliments and threats. In August 2020, Chinese media praised South Korea’s efforts to "be objective and keep its friendship with China," and several weeks later, Chinese scholars commended South Korea’s “kindness to China” in a time of “U.S. suppression.” But after South Korean President Moon Jae-in discussed Taiwan with Biden at their May 2021 summit, China’s Foreign Ministry warned South Korea not to “play with fire.” It is telling that Chinese scholars at a government-affiliated institute are arguing openly that China needs to raise the cost of South Korea’s cooperation with the United States on Taiwan.

North Korea’s missile capabilities are helping accomplish this task. The newer rockets more effectively threaten South Korea, and they increase Seoul’s doubts about the efficacy of U.S. deterrence. North Korea has explicitly tied its menacing assets to the issues surrounding the island. Pyongyang has publicly criticized the United States policies’ on Taiwan and threatened that “tragic consequences” will result from U.S. support. “The indiscreet meddling by the U.S. into the issue of Taiwan entails a potential danger of touching off a delicate situation on the Korean peninsula,” North Korea’s vice foreign minister said in a statement. These words could make Seoul think twice about backing the United States in the Taiwan Strait.

Japan is more difficult to split from Washington. But North Korea’s activities can certainly draw some of Japan’s attention away from Beijing. Although Tokyo was getting onboard with playing a greater role in deterring China and defending Taiwan, Japan’s Ministry of Defense has identified North Korea’s military capabilities as a “grave and imminent” threat, and there is no doubt that the government’s focus will shift if Pyongyang escalates its provocations. In the White House’s statement regarding Biden’s January 21 meeting with Japanese Prime Minister Fumio Kishida, Taiwan was mentioned only once. In comparison, the two leaders cited North Korea three times, condemned the country’s recent missile tests, and committed to work with South Korea more closely. Although Tokyo could theoretically focus on both North Korea and China, in practice it might struggle. Pyongyang poses a far more direct threat to Japanese lives and territory than does Beijing, and it would be hard for Japanese leaders to concentrate on China if North Korea grows more belligerent.

Drawing the Heat

North Korea’s new capabilities don’t help Beijing just diplomatically. The tests provide tangible, military benefits. The United States has been attempting to enlist South Korea in its efforts to strengthen deterrence across the Taiwan Strait. But Pyongyang’s new missiles mean Seoul is less likely to focus its military somewhere other than North Korea, especially if it continues the provocations. Indeed, a South Korean expert on Chinese politics has argued that when Washington asks for support in its contest with Beijing, Seoul should explain that it is too busy handling Pyongyang.

To reassure its allies, the United States may also need to refocus military attention on the Korean Peninsula, reducing its ability to operate in other parts of Asia. In 2017, when North Korea conducted ICBM and nuclear tests, the United States responded by sending more strategic assets, including heavy naval power, near the Korean Peninsula. If tensions rise high enough, Washington may have to do so again, including by shifting the Seventh Fleet’s operational focus to the area. Stationed in the middle of Japan, this fleet has been one of the United States’ primary tools for deterring Beijing, conducting patrols near the Taiwan Strait and promoting freedom of navigation in the South China Sea. But given past positioning patterns, a crisis on the Korean Peninsula would also most certainly drag the fleet farther north, undermining Washington’s ability to carry out operations elsewhere.

A major war on the Korean Peninsula would prove particularly devastating to the United States’ competition with Beijing. In addition to the Seventh Fleet, the United States Forces Korea’s 28,000 soldiers, 40 F-16 fighters, 90 military aircrafts, 40 attack helicopters, and other assets would immediately become unavailable for operations beyond the peninsula. A majority of the United States Forces Japan’s aircraft, ships, and approximately 55,000 military personnel would also be deployed to Korea. Japan’s own military, which could help the United States if it needed to fight China, would grow busy providing combat support to protect U.S. naval forces—including antisubmarine operations and sea minesweeping—as U.S. troops prepared for an amphibious landing on the peninsula.

Beijing, by comparison, is in a better position. The United States has to worry that China will use a North Korea–spurred crisis to invade Taiwan, but the inverse isn’t true: Beijing isn’t concerned that Seoul or Washington will start a war over Taiwan if Pyongyang launches an attack. China’s commitment to North Korea is also not as comprehensive as the United States’ is to Seoul. In the event of a renewed Korean war, China plans to send mostly ground forces into the North. Its air and naval assets would remain focused across the Taiwan Strait.

For China, therefore, a crisis on the peninsula—especially one that evolves into a conflict—would be a golden opportunity to expand its power. It may even make it possible to defeat Taipei. With U.S. intelligence assets supporting troops in Korea, a Chinese amphibious force might be able to move on the island without giving the United States advanced warning. China could establish beachheads on Taiwan long before U.S. forces, bogged down on the peninsula, have time to arrive. The war’s eventual outcome would be a fait accompli.

North Korea’s latest tests may have already made a Chinese attack more likely. As Chinese media happily pointed out, Pyongyang’s January 11 missile launch briefly confused the United States Northern Command’s warning system, grounding some commercial airplanes for 15 minutes. China has the most advanced ballistic and cruise missile program in the world. If North Korea’s offensive strike capability can jeopardize the U.S. early warning system, it surely bodes well for Beijing’s ability to surprise and defeat Washington’s forces.

Better Together

To counter North Korea’s new missile threats and prevent them from helping China, the Biden administration needs a stronger North Korea strategy—one that deters further provocations, reassures South Korea, and demonstrates Washington’s continued resolve and credibility to Beijing. That means Washington must support South Korea’s efforts to advance its offensive capabilities, such as the development of nuclear-powered submarines. South Korea, meanwhile, must scale up its combined exercises with the United States. A stronger U.S.–South Korean alliance will improve the two countries’ combat readiness, which is especially critical at a time when North Korea appears to be building up to another round of ICBM and nuclear tests. Finally, closer ties would make it easier for the United States to marshal allies in its competition against China, including in the Taiwan Strait.

The United States should also use the renewed tensions on the Korean Peninsula to encourage closer Japanese–South Korean cooperation. Seoul has long had highly fraught relations with its former colonial ruler, and the two states have especially struggled to get along in recent years. But for better or worse, the Korean Peninsula, East China Sea, and Taiwan Strait are increasingly intertwined in the current era of strategic competition. Pyongyang's provocations against the United States and its allies on the peninsula can embolden the Chinese Communist Party to act in other regions. And if Beijing can weaken or defeat the United States and its Asian allies anywhere, both the Chinese Communist Party and the Kim regime will be emboldened to act on the peninsula. To cope with this changing security environment, it makes sense for strategists in Washington, Seoul, and Tokyo to package these issues together. By demonstrating greater coordination, the three countries would also make it harder for China or North Korea to fracture Washington’s East Asia alliances, regardless of the contingency.

Finally, these three states must prepare for simultaneous provocations in East Asia, including concurrent conflicts in Taiwan and on the Korean Peninsula. In consultation with one another, the United States and its allies must demonstrate a strong willingness to cooperate and take strategic risks. They should hold more trilateral defense minister meetings, more thoroughly review various contingency scenarios, and discuss how to enhance their combined capabilities. Hopefully, these countries will never need to put these plans and abilities into practice. But to deter Kim Jong Un and Xi Jinping, they need to prove that they can fight two wars—and win both—if the need arises.