A Two-Front Risk

Potential for conflict in Taiwan Strait causing increased concern in Seoul

Ashton Cho

War breaking out in the Taiwan Strait would not pose a direct national security threat to South Korea. The secondorder consequences, however, would be significant. From the perspective of the Republic of Korea (ROK), a potential Taiwan conflict demands two levels of national security assessments, leading to the conclusion that, as a treaty ally of the United States, it would be incumbent upon the government in Seoul, as well as the ROK Armed Forces, to proactively define a Taiwan strategy.

While South Korea would not be in the line of fire should Beijing order the People’s Liberation Army

(PLA) to march on Taiwan, and hence would not be mobilizing its defenses to exchange direct fire with Chinese troops, leaders in Beijing must surely be apprehensive about such a move provoking more states than is absolutely necessary. Beijing is doubtless waiting for the opportune moment when conditions are right—such conditions being when the PLA reaches sufficient war fighting capabilities; when domestic political conditions align; and when the resolve of the United States and its allies is at an ebb, even if only momentarily. At that point, a PLA blockade, assault, or full-scale invasion of Taiwan will most likely be executed in a manner designed to avoid provoking

Dr. Ashton Cho is the director of international security cooperation at the Korea Association of Military Studies and is currently a Taiwan Fellow at the ROC National Defense University. He can be reached for comment at ashtonscho@gmail.com other states—especially not South Korea.

South Korea and its formidable military are located across the Yellow Sea from China. The ROK Navy’s Second Fleet has significant real-world combat experience due to periodic North Korean aggression on the Northern Limit Line that divides the maritime boundary between the north and south. Examples include the first and second Battles of Yeonpyeong in 1999 and 2002. This puts the PLA’s Northern Theater Command directly across the Yellow Sea from two American military posts near the west coast of South Korea: the Kunsan K-8 Air Base and Osan Air Base. While South Korean governments have historically opposed the use of US Forces Korea (USFK) in deployments outside of the peninsula, it is no secret that the United States has been increasingly calling for the USFK to have more strategic flexibility in recent years.

One of the worst-case scenarios for the Chinese Communist Party (CCP) would be the USFK’s rapid deployment to Taiwan. This would drastically heighten the chances of the ROK-US mutual defense treaty being activated, which would force the PLA to deal with the combined forces of the ROK and US militaries.

From South Korea’s perspective, a Taiwan conflict and a confrontation with China is best avoided for two main reasons. First, South Korea’s primary and existential threat is the Democratic People’s Republic of Korea (DPRK). On the Korean peninsula, over a million DPRK troops and hundreds of thousands of ROK troops stand face-to-face in a Korean War that has not ended, but has merely been set on pause with the Korean Armistice Agreement of 1953. With North Korea’s large inventory of long-range artillery that puts the security of Seoul and the lives of tens of millions of people at immediate risk, a complete array of ballistic missile capabilities, and the DPRK’s willingness to use them, plus an estimated 40 to 50 nuclear warheads, the scale of destruction in a potential resumption of the Korean War is unparalleled.

Increased belligerence

Kim Jong Un, the Supreme Leader of North Korea’s hereditary authoritarian dictatorship, has also proved to be much more aggressive than either his father or his grandfather. Just a few decades ago, an average of one ballistic missile was tested per year. In 2022 alone, however, North Korea conducted over 90 ballistic and cruise missile tests. Within 12 years under his rule, the Marshall, as Kim is known, has already conducted four nuclear weapons tests, one of which is claimed to have been a thermonuclear hydrogen bomb. Clearly, it is North Korea’s capabilities—and the political leadership behind those capabilities, with all the attendant actions and rhetoric—that make the DPRK the top national security priority for South Korea, putting China a distant second. flict, might undermine the readiness of the combined ROK-US defense posture against North Korea, and could make the Korean peninsula an attractive military target for the PLA. Moreover, as per the ROKUS mutual defense treaty, if US troops are attacked in the Indo-Pacific, Seoul is obliged to come to their defense. This would spread ROK military forces thin, in addition to putting them in direct confrontation with the PLA.

The other reason that Seoul wishes to avoid a crossstrait conflict is that US military involvement in a Taiwan war would undermine the security of South Korea. USFK’s direct deployment in a Taiwan war, or the use of US bases in Korea to conduct direct operations or provide logistical support in a Taiwan con-

These reasons might help explain the reluctance by Korean administrations to take an official position on the Taiwan question. As a reminder, current ROK President Yoon Suk-yeol was the only leader not to meet with US Speaker of the House Nancy Pelosi during her August 2022 trip to Asia, which included the contentious visit to Taiwan. Also, in stark contrast to Washington’s Indo-Pacific allies such as Tokyo and Canberra, which have increasingly voiced strong support for the security of Taiwan, Seoul has remained almost completely silent.

If China wishes to avoid provoking South Korea, and South Korea wishes to avoid having to intervene in a Taiwan conflict, it is worth re-examining whether South Korea’s political silence, as well as its regional military isolationism, best serve its national interests.

A country-to-country dyadic threat assessment like the one above is important, but it is incomplete on its own. The Indo-Pacific region is populated by some of the world’s top military states and most robust economies. South Korea, despite having the eighth-largest military and 13th-largest economy in the world, is a middle power. Given South Korea’s middling position in the Indo-Pacific strategic-military landscape, the most important variable affecting national security is not North Korea, but the intensity and scope of the competition and confrontation between the United States and China.

As such, when it comes to South Korea’s most immediate threat (North Korea), the ROK’s ability to deter the DPRK is importantly a function of US commitment to the combined defense posture, as well as the credibility of its promise of extended deterrence. This is a function of how the United States calculates the distribution of capabilities and commitments in the Indo-Pacific theater—specifically the USINDOPACOM force posture. More immediately, the effectiveness of economic sanctions against North Korea, and the range of available diplomatic options to engage with Pyongyang, are a function of the state of US-China relations. Seoul’s North Korea policy varies greatly according to which political party is in power, the level of the North Korean threat, and the given state of the US Indo-Pacific strategy and posture—one that is primarily built around deterring a rising China.

Second-order consequences

If politicians in Seoul assess that the risk of US and Chinese forces coming to blows in a Taiwan war is too high, they must gauge the second-order national security consequences of how such a confrontation would affect South Korea’s national interests. Political silence may be diplomatically palatable and expedient now, but proper threat assessments, contingency planning, and related exercising and training must begin to take place eventually.

Second-order national security threat assessments are necessary and unavoidable, for any country. South Korea’s mutual defense treaty with the United States makes this doubly important. While every middle or small nation in the Indo-Pacific region would be wise to make national security assessments and enact contingency plans to deal with the increasing risk of a US-China confrontation, this is of paramount importance for South Korea because our fates are interlinked as America’s most integrated bilateral military ally.

In short, because South Korea is a treaty ally with the United States, and US-China relations are deteriorating in a manner that makes confrontation more likely to occur over Taiwan, South Korea’s national security is indirectly—but no less importantly—affected. While a more comprehensive assessment is needed, a first-cut, second-order consequence analysis would suggest there are two categories of how a Taiwan Strait confrontation would affect South Korean national security.

The first category is the ROK military’s role in America’s Indo-Pacific strategy, undergirded by the mutual defense treaty. The Biden administration is actively looking to move away from the traditional hub-and-spokes alliance system and link the “spoke” countries together, thereby multilateralizing the re- gion’s hitherto bilateral security architecture. For northeast Asia, this means strengthening security cooperation between the ROK, Japan, and also Taiwan in preparation for contingencies in three specific hotspots: the Taiwan Strait, North Korea, and the Senkaku Islands.

As for the USFK, the increasingly stronger calls for strategic flexibility have been met with hints that President Yoon, while resistant, might be willing to consider US proposals. Beyond the bottom-line scenario that the ROK is obliged to come to the aid of US forces if they are attacked, wider alliance readjustments will have to be made regarding Taiwan. This implies a delicate balancing act between, on the one hand, the rise in the strategic value of ROK bases for the United States that also increases ROK vulnerability to the PLA, and, one the other hand, the ROK’s need for a stronger US commitment against a more provocative North Korea, which by many measures is a de facto nuclear weapons state.

The second category is anticipating China’s strategy and actions in response to the US Indo-Pacific strategy, which includes South Korea. While China might wish to avoid provoking South Korea and facing the ROK-US alliance, if it expects to confront a network of US allies and partners over Taiwan, China would be prudent to devise plans against the ROK military. South Korean policy makers should, together with their US and regional counterparts, jointly prepare for a potential PLA confrontation with the ROK military. A few possible scenarios require immediate attention.

First, in a Chinese attack on Taiwan, there is the potential that Beijing will coordinate with Pyongyang to open a second front on the Korean peninsula. Even without a high level of aggression, such a North Korean provocation on the peninsula would tie down USFK troops and divert important US assets, including some of those based in Japan, away from the Taiwan front. The ROK military must plan and prepare for this contingency. Second, what role will the PLA’s Northern Theater Command play in a Taiwan war? It might be tasked to augment the forces of the Eastern Theater Command. Alternatively, it could be deployed to deter the ROK Navy Second Fleet and US Air Force from entering the Taiwan Theater. The alliance must study these contingencies and develop an ROK-US joint response plan.

It is not in South Korea’s national interests to intervene in a Taiwan war and confront the PLA. It is also not in South Korea’s national interests for the United States to intervene in a Taiwan war. This is because South Korea’s primary national security threat is, and must remain, the DPRK, and US intervention in Taiwan may undermine the ROK-US combined deterrence against North Korea. Naturally, this position must be balanced against the costs of a Chinese attack on Taiwan that goes unanswered. How would South Korea fare in an Asia-Pacific in which the CCP projects power out to the second island chain?

A key variable in South Korea’s geostrategic landscape is the nature and intensity of US-China relations. With the United States and China taking a more confrontational approach to each other—especially over Taiwan—this situation gives rise to a series of non-trivial second-order security threats and risks that South Korea must jointly assess, jointly plan, and jointly exercise and train for with the United States, but also key regional partners like Japan, and Taiwan. n

Strategic Vision vol. 12, no. 55 (April, 2023)