With Donald Trump’s victory in the U.S. presidential election, America First is expected to resurface, signaling a second seismic shift in the international security landscape. Trump, who views alliances from a transactional perspective, has made it clear that the United States will no longer bear the sacrifices of being the world’s sole policeman. His administration is likely to prioritize clear national interests over the abstract goal of restoring U.S. leadership. By operating under the framework of power politics among great powers and striving for “fair” alliances, Trump aims to maintain the United States’ leading position in the international community while pursuing economic prosperity.
 

The Diplomatic and Security Renewal in Trump’s Second Term

 
The core of Trump’s security policy is the realization of peace through strength. Ensuring peace entails a readiness to go to war if peace cannot be guaranteed. To achieve this, robust economic power and overwhelming military strength are essential. Trump has maintained a transactional perspective, extending from trade to alliances, to meet these goals. Therefore, Trump’s MAGA diplomatic and security “doctrine” can be characterized as “practical transactionalism.”

If Trump’s first term was a period of introducing the concept of “peace through America First,” the second term would be the time to establish a diplomatic and security policy based on practical transactionalism. The top priority remains China, while Middle East policies sidelined under the Biden administration are expected to gain greater prominence. However, urgent tasks such as resolving the Ukraine war and the Hamas conflict must be addressed first. Given his repeated campaign promises for swift resolutions, these issues will be a clear demonstration of the diplomatic capabilities of Trump’s second term. Meanwhile, the question of who will bear the efforts and costs in advancing this Trump-style peace policy is critical. As a result, the transfer of costs and burdens to allies is expected to continue increasing over time.

China will remain the top priority on Trump’s foreign and security agenda. However, concluding the Ukraine war and the Israel-Hamas war will take precedence. The second Trump administration is expected to promote ceasefires in both wars, reducing America’s level of involvement. In Europe, NATO will be expected to assume greater responsibility for deterring Russia and managing the Ukraine war. In contrast to the Biden administration, Trump’s Middle East policy is anticipated to become more proactive, focusing on pressuring Iran with Israel at the center.

On the Korean Peninsula, Trump’s security policy may retain its fundamental stance, but it differs significantly in implementation. While the Korean Peninsula remains subordinate to China policy, the conditions have shifted due to South Korea’s expanded international role, North Korea’s strengthened nuclear capabilities, and the Ukraine war. Above all, the South Korean government now pursues a Korea-led response in negotiations and strategies with North Korea, contrasting with the situation during Trump’s first term. If the United States unilaterally advances its inter-Korea policy, it could lead to conflicts with its ally, South Korea.
 

Policy Implications for South Korea

 
Resolving issues like defense cost-sharing or the reduction of U.S. Forces Korea (USFK) will require a deeper understanding of the U.S.’s desire for fundamental alliance restructuring. First of all, the United States and South Korea concluded the 12th Special Measures Agreement (SMA) on October 14, 2024, finalizing the defense cost-sharing arrangement. However, the Trump administration could easily overturn the SMA, as it is merely an administrative agreement for the United States. However, if a new “Extended Deterrence Contribution Fund” is created with additional budgetary contributions to secure nuclear weapons dedicated to the Korean Peninsula and expand U.S. strategic assets on the Peninsula rather than overturning the existing agreement, it will equate to endowing the United States with an unprecedented gift while substantively strengthening the existing ROK-U.S. nuclear joint planning and the Nuclear Consultative Group (NCG).

The reduction of USFK could be substituted with enhancing the flexibility of these forces. Recognizing that further reductions in the US Army in Korea might impair ground forces’ functionality during wartime, the focus could instead shift to improving the regional deployment capabilities of USFK, potentially attracting additional troops. For instance, U.S. Marine Corps units could be further stationed in Pohang or Jeju while ports such as Busan or Gangjeong could be shared as bases for U.S. naval forces, simultaneously bolstering anti-North Korea amphibious capabilities and Indo-Pacific deployment capacity.

Taking it a step further, the ROK-U.S. alliance could consider expanding its operational scope across the region. For example, the International Peace Supporting Standby Force by ROK Army Special Warfare Command, the Army’s 2nd Rapid Response Division, or the South Korean Marine Corps could be offered as Quick Reaction Forces (QRFs) in the Indo-Pacific region. Although Japan is enhancing its military capabilities alongside the United States to respond to potential Taiwan contingencies, the constraints of its pacifist constitution and the passive stance of its Self-Defense Forces cast doubt on its effectiveness as a practical deterrent. Conversely, the well-coordinated ROK-U.S. rapid response forces, with their extensive history of joint training and operations, could play a significant role not only in deterring North Korea but also in maintaining peace across the Indo-Pacific region.

Meanwhile, South Korea could make significant contributions to the U.S. military rebuilding efforts. During Trump’s first term, he proposed building a 350-ship fleet but failed to meet this goal due to budget constraints and the limited shipbuilding capacity of the U.S. industry. In a recent congratulatory call with President Yoon Suk-yeol, Trump mentioned South Korea’s shipbuilding capabilities and sought cooperation. If South Korea could provide maintenance and construction of new U.S. Navy vessels with reduced budgets—something the declining U.S. shipbuilding industry struggles to handle—South Korea could establish itself as an indispensable ally in achieving America’s core interest of military reconstruction.