During his two years in office, South Korean President Yoon Suk Yeol has espoused the need to uphold a rules-based international order and maintain a free and open Indo-Pacific. He rejected his predecessor’s timid fence-sitting policy of trying to balance South Korea’s security and economic relationships with the United States and China. Instead, Yoon declared that South Korea must never compromise on its core security interests and vowed to strengthen its alliance with the United States to counter the growing Chinese threat to the region.

In response to growing fears of Chinese military action against Taiwan, Yoon pledged South Korea would assume a greater international security role and join multilateral initiatives to defend democracies against attack or coercion. Seoul gradually became more forthright in articulating its concerns about a potential military contingency in the Taiwan Strait and increasingly defined Taiwanese security as directly affecting that of South Korea.

Yet, despite this new-found advocacy for regional security, South Korea remains reluctant to criticize China directly or define the measures it would undertake to uphold those values against regional threats. Seoul remains reluctant, if not resistant, to defining the role it would play if China were to invade Taiwan. Seoul’s reticence is due to its focus on the existential North Korean threat, fear of economic retaliation from China (its largest trading partner) and the perception that Taiwan is far away and not a South Korean responsibility.

Chinese action against Taiwan, however, would have significant and potentially cataclysmic impacts on South Korea’s economy and security. South Korea’s economy is heavily reliant on trade, supply chains and maintaining freedom of navigation for imports and exports. South Korea and Taiwan are each other’s fifth-largest trading partners. More than 90 percent of South Korea’s maritime trade volume passes through the Taiwan Strait and the South China Sea. A China–Taiwan conflict could reduce South Korea’s GDP by an estimated 23.3 percent.

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Beyond the physical and economic devastation of a military clash, a Chinese victory over Taiwan would enable Beijing to subsequently project military power against and undermine the security of other Indo-Pacific democracies, including South Korea and Japan. A dominant Chinese sphere of influence would incentivize Beijing to dictate terms to its neighbors, which would be less able and willing to resist Chinese coercion.

There would certainly be risks for South Korea to become involved in a multilateral coalition to defend Taiwan. China may inflict economic retaliation or even attack U.S. or South Korean bases. However, there are also tangible costs of not supporting an international defense of Taiwan. South Korean reluctance to defend Taiwan could have significant repercussions for its alliance with the United States as well as international support for Seoul after a North Korean attack.

U.S. policymakers and the American public might question the continued value and relevance of its military relationship with South Korea if Seoul attempts to sit on the sidelines. A South Korean refusal to defend U.S. forces could be seen as a failure to abide by, or an abrogation of, the mutual defense treaty. Such inaction by South Korea would likely end the alliance.

If China attacked Taiwan, South Korea would be expected to participate in international sanctions against Beijing, impose its own unilateral economic punitive measures including trade bans and denial of Chinese ships and planes transit of Korean airspace or entry into Korean ports, allow the U.S. forces in South Korea to engage in Taiwan operations and endorse—if not participate in—an international military response.

While few U.S. officials or experts advocate a direct South Korean military role in or near Taiwan, American expectations are that Seoul would need to assume greater responsibility for its own defense against North Korean contingencies, conduct intelligence, surveillance and reconnaissance against Chinese ships and planes operating near the Korean Peninsula, provide enhanced rear-area and logistical support to U.S. forces and enhance protection to U.S. military units against Chinese attacks.

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Regional security threats require regional responses. There is a clear need to augment Indo-Pacific military capabilities, increase reserves of ammunition and missiles, assist less-capable nations in security capacity-building and strengthen multilateral coordination and integration of intelligence-sharing and contingency planning. The United States and its regional partners should increase communication, intelligence-sharing and operational contingency planning with Taiwan.

The U.S. should intensify its efforts to expand military co-development and co-production with allies and partners to replenish depleted reserves and prepare for potential conflicts in the Indo-Pacific. South Korea is an obvious candidate given its world-class defense industry, highly advanced production capabilities and long-standing military relationship with the United States.

Yoon needs to publicly underscore the strategic importance of Taiwan to South Korean national interests. The Yoon administration should engage with and educate the populace on the consequences to South Korea if China were successful in dominating Taiwan through economic coercion, low-intensity conflict or large-scale military force.

While South Korea must understandably remain predominantly focused on the North Korean threat, Seoul must be prepared to assist the international community to protect its strategic interests in the Indo-Pacific. Seoul has a formidable, highly capable military to implement President Yoon’s pledge for his country to become a Global Pivotal State by shouldering greater responsibilities for addressing regional security challenges.