Here's What You Need To Remember: The original Korean War - from 1950 to 1953 - was horrific, but it was a limited war that was confined to the Korean Peninsula and did not involve the use of nuclear weapons. A second Korean War has no such guarantees.

War on the Korean Peninsula is almost too horrible to contemplate.

Nuclear-armed adversaries, fighting in densely populated urban terrain, could cause humanitarian disaster on a scale that the world has never seen. But the scenario might grow even worse. The last time that the United States fought North Korea, the People’s Republic of China intervened with destructive effect. The war lasted for three years, with heavy casualties on both sides. While both China and the United States have worked hard to prevent a recurrence of this catastrophe, the two great powers remain at odds over the fate of North Korea, a disagreement that might yet lead to war.

How it Happened Before:

The United States and China were not supposed to go to war in 1950. The war resulted primarily from U.S. miscalculation of Chinese intentions and capabilities; U.S. forces failed to detect the movement of significant People’s Liberation Army (PLA) forces into Korea, failed to pay sufficient attention to Chinese signals, and lacked a good understanding of Communist China’s nascent diplomatic efforts. Chinese intervention was an operational surprise that should not have been, successful in throwing U.S. forces out of North Korea and restoring something close to the antebellum status quo. The first Korean War did not work out well for either country, although both the United States and China successfully maintained the independence of their respective proxies.

How it Could Happen Again:

War in Korea could resume for any number of reasons; even a collapse of the North Korean regime could start a race for Pyongyang that produced great power conflict. Over the past year, however, tensions have grown over the extent and progress of North Korea’s nuclear and ballistic missile programs. The United States sees these (and North Korean bombasticity) as a threat, and the North Koreans see U.S. threat-mongering as the potential prelude to war. This leaves both sides with ample incentive to launch a preemptive war against the other. Thus, war between the U.S. and the DPRK could plausibly begin with either a North Korean attack on South Korea or Japan, or a U.S. attack on North Korea.

China is unlikely to view U.S. response to a North Korean attack as legitimate cause for war, unless that response crosses certain red lines. These red lines could be similar to those that the PRC laid down in 1950, although both Chinese fear of the United States and Chinese affection for North Korea have declined over time. Similarly, the United States probably will not see any upside in pre-empting Beijing’s response by directly attacking China. Still, Beijing has little interest in seeing U.S. forces along the Yalu River. If China believes that the United States foolishly blundered into a war, or pushed North Korea into a pre-emptive war through brinksmanship, then Beijing’s attitude could become more belligerent. Moreover, China might view a U.S. attack on North Korea as an indicator of incorrigible aggression, evidence that the United States truly is a “rogue nation” as likely as not to attack China at some point in the future.

As a prelude to intervention, China would begin to signal its disfavor by elaborately visible military preparations, as well as diplomatic condemnations. The Trump administration undoubtedly runs some of the same risks of misinterpreting Chinese statements as the Truman administration did in 1950. The US could properly read these signals as indications of China’s willingness to commit, or it could misread them as bluster. At the same time, if Beijing was serious, it would begin quietly redeploying long-range assets away from Korea, into relatively safe locations in China’s interior. The PLA faces the dilemma of needing to reduce the chance of war, while at the same time maximizing its chance of victory.

How it Could Play Out:

If war starts with a Chinese response to a perceived U.S. provocation, the PRC will initially confine its activities to the Korean Peninsula. Beijing will want to send a message of seriousness to Washington without opening up a wider war, in the hopes that the Trump administration will restrain itself from further aggression. Chinese ballistic missiles and cruise missiles (launched from air and land platforms located as deep as possible within China, in order to avoid offering easy targets to the US) will strike US and South Korean military installations, including airbases, communications centers, and logistics facilities. If U.S. and ROK forces have advanced into North Korea, China will likely focus on forward deployed assets, although the PLA will not want to waste valuable munitions on conventional forces along the front.

This strategy essentially worked in 1950; the United States refrained from attacks against the Chinese mainland, did not mobilize Japan militarily, did not “Unleash Chiang” from his Formosan stronghold, and did not use nuclear weapons. Instead, the combatants waged war in conventional means up and down the peninsula, a matchup which did not equalize the playing field but did give the PLA its best hope of victory.

But if China and the United States did become engaged in active combat operations against one another in Korea, it is unlikely that the fight would stay confined. The U.S. military would face an enormous temptation to directly airbases, missile installations, and staging areas in China, while attacks US bases across the region would undoubtedly tempt China. Changes in military technology have altered the nature of distance in warfare; Chinese and American missile sites can hit targets in Korea from vast distances, and commanders would be tempted to attack enemy staging and launch areas in depth. Moreover, the huge Chinese reconnaissance-strike complex, laid out over a vast expanse of space, air, sea, and land, would immediately become the subject of US attentions. In particular, the U.S. might see fit to convey its own seriousness by launching attacks against major Chinese naval vessels, including aircraft carriers, destroyers, and nuclear submarines.

Parting Thoughts:

War between the United States and China in Korea is unthinkable, but not impossible. Therefore, we have to think about it. While the first Korean War represented a failure of diplomacy and strategic planning, Washington and Beijing nevertheless managed to confine the conflict, and limit the extent of escalation. Whether they would be able to do so in 2017, after dramatic changes in the geopolitical situation, is a different question entirely.

In case war breaks out (either at the instigation of Pyongyang or Washington), American and Chinese diplomats need to go into overdrive in order to ensure good communication between the two capitals. The vast commercial interests that depend on the health of U.S.-China trade need to make their voices heard in both China and the United States. And if war does happen, policymakers on both sides need to work hard to limit the extent of destruction, whatever cold comfort this may provide to the victims of the war on the Korean Peninsula.

Robert Farley, a frequent contributor to TNI, is author of The Battleship Book. He serves as an senior lecturer at the Patterson School of Diplomacy and International Commerce at the University of Kentucky. This piece was originally featured in October 2017.

Image: Reuters.