The only thing more alarming than a military confrontation between the U.S. and North Korea (the DPRK) would be a military confrontation between the U.S. and China. Yet as tensions between the United States and the DPRK continue to rise, too few analysts are considering the danger of China intervening militarily in response to a U.S. strike on the DPRK’s nuclear weapons and missile programs. This oversight is surprising, especially given that China is legally obligated to render military assistance to North Korea if the U.S. launches any kind of armed attack.
The Contracting Parties undertake jointly to adopt all measures to prevent aggression against either of the Contracting Parties by any state. In the event of one of the Contracting Parties being subjected to the armed attack by any state or several states jointly and thus being involved in a state of war, the other Contracting Party shall immediately render military and other assistance by all means at its disposal.
Article 2 is not a paragon of clarity. A “state of war” (战争状态时) is not defined by the treaty and, more generally, is not a meaningful term under the laws of war. “Other assistance” and the type of military aid to be provided are also not specified. Nevertheless, the article’s meaning, given its construction in the original Chinese, is quite clear—any armed attack against North Korea requires a military response from Beijing as well as other assistance.
Indeed, Article 2 arguably imposes a greater legal obligation on China to defend the DPRK than the U.S. has undertaken in any of its mutual defense agreements. For instance, Article 3 of the 1954 U.S.-South Korea Mutual Defense Treaty states:
Each Party recognizes that an armed attack in the Pacific area on either of the Parties in territories now under their respective administrative control, or hereafter recognized by one of the Parties as lawfully brought under the administrative control of the other, would be dangerous to its own peace and safety and declares that it would act to meet the common danger in accordance with its constitutional processes.
The U.S.-ROK treaty is thus full of limitations on U.S. obligations to defend South Korea that do not exist in the China-DPRK treaty: 1) it applies only in the Pacific; 2) it applies only to attacks on the Parties in “territories under administrative control”; 3) it requires only “act[ing]… in accordance with  constitutional processes.” There is no specific requirement that the U.S. even provide military assistance to South Korea, much less the “immediate… military assistance… by all means at its disposal” that China has promised the DPRK.
Nonetheless, a number of Chinese scholars have argued that China is not obligated to defend North Korea under the treaty if the U.S. launches a preemptive strike on North Korea’s nuclear weapons programs because North Korea’s development of nuclear weapons relieves China of its military obligations. This interpretation is a stretch. It is true that Article 1 commits both countries to “continue making every effort to protect peace in Asia and across the world as well as the safety of each country’s citizens.” But there is no evidence that this treaty language was meant to prevent the development of a given weapons technology. North Korean officials, furthermore, have justified their nuclear weapons program as a self-defense measure after the recent U.S. strike on Syria.
Other scholars have argued that China would be required to assist only if land forces invaded North Korea. Nothing in Article 2, however, suggests that the phrase “armed attack” must be interpreted in this limited way. The term is likely drawn from Article 51 of the U.N. Charter, which recognizes a right to collective self-defense in response to an “armed attack.” Most countries, including the United States and China, would almost certainly treat a missile strike or bombing raid as an armed attack triggering the right to self-defense under the U.N. Charter Bonnie Glaser of CSIS, furthermore, has reported that Chinese officials have unsuccessfully tried to convince Pyongyang to remove the treaty’s Article 2 mutual defense obligations. These requests strongly suggest that China understands that it is still obligated, as a matter of treaty law, to respond to an armed attack against North Korea with “immediate military assistance.”
We do not claim that the mere existence of a treaty obligation will force China’s military involvement in the DPRK against its will. But the treaty is not a meaningless Cold War relic either. This past year, Presidents Kim and Xi exchanged friendly public letters marking the 55th anniversary of the treaty. Some in China have called on China to terminate the DPRK defense treaty, but a selection of Chinese experts surveyed by the Chinese newspaper Global Times last year continued to support the treaty alliance despite growing reservations.
In the end, Chinese officials could always ignore their treaty obligations or choose to adopt an implausible interpretation to avoid getting involved in a U.S.-DPRK conflict. However, abandoning the treaty or failing to fulfill the treaty’s terms would not be costless for the Chinese leadership’s reputation at home or abroad. U.S. analysts should keep this in mind when weighing China’s all-important reaction to any U.S. strike on North Korea.