U.S. Defense Strategy Omits Extended Deterrence, Targets China [Yang Nakkyu's Defence Club]

A Reversal from Previous Administration’s Strengthening of the U.S.-ROK Alliance
China Prioritized as Top Threat, First Island Chain Strategy Takes Precedence

The latest U.S. National Defense Strategy (NDS), which outlines the defense policy direction for the second Trump administration, has drawn attention for omitting any mention of "extended deterrence," a term referring to the provision of a nuclear umbrella to allies. This stands in stark contrast to the previous U.S. stance of emphasizing the U.S.-South Korea alliance and pledging to strengthen extended deterrence.

Elbridge Colby, Deputy Assistant Secretary of Defense for Policy at the U.S. Department of Defense, who is visiting Korea, is delivering a keynote speech at the Sejong Institute in Jongno-gu, Seoul, on the 26th. Photo by U.S. Forces Korea. Yonhap News Agency

According to the NDS released on the 23rd (local time), "extended deterrence," which means providing allies with nuclear deterrence equivalent to that of the U.S. mainland in addition to conventional deterrence, was not specified. Instead, the NDS defined the Western Hemisphere-including North and South America and Greenland-as de facto "homeland," and presented its defense as the top priority under what it calls the "Donroe Doctrine." Key elements for homeland defense included the "Golden Dome," a next-generation missile defense system proposed by Trump, as well as responses to narco-terrorists and the use of advanced drones to defend U.S. airspace.

Regarding the operation of U.S. nuclear forces, the NDS simply stated, "We will maintain a robust and modern nuclear deterrent capable of responding to strategic threats to our country." Overall, the document offered less detail than in the past about how the U.S. would use and modernize its nuclear arsenal, and omitted any reference to extended deterrence for the defense of allies.

Focus on Nuclear Modernization, Not Extended Deterrence

Extended deterrence is the U.S. commitment to provide allies with a level of nuclear deterrence equivalent to that of the U.S. mainland. This concept adds conventional weapons and missile defense to the nuclear umbrella, declaring that if a potential adversary attacks an ally with nuclear weapons, the U.S. will mobilize all its capabilities for retaliation, thereby deterring aggression. The U.S. formalized its nuclear umbrella commitment to South Korea in 1978, and pledged extended deterrence after North Korea's first nuclear test in 2006.

In the previous NDS released under the Biden administration in 2022, the document stated, "The Department of Defense will continue to modernize nuclear weapons, the ultimate backstop for deterring attacks on the U.S. homeland and on our allies and partners who rely on U.S. extended deterrence," and made clear its policy of strengthening extended deterrence.

U.S.-South Korea Channels Remain Open... Not a Complete Abandonment of Extended Deterrence

However, the Trump administration has not officially abandoned its extended deterrence commitment to allies. The Joint Fact Sheet released last November, which included the results of the summit between President Lee Jaemyung and President Donald Trump, reaffirmed that "the United States commits to providing extended deterrence, utilizing the full range of its capabilities, including nuclear weapons."

In addition, the joint statement from the 57th U.S.-South Korea Security Consultative Meeting (SCM) in the same month included language that "(Pete) Hegseth, U.S. Secretary of Defense, reiterated the U.S. firm commitment to provide extended deterrence to South Korea by employing the full range of U.S. military capabilities, including nuclear weapons." Last month, the Nuclear Consultative Group (NCG), a U.S.-South Korea consultative body on extended deterrence, convened for the first time since the launch of the second Trump administration. These agreements and ongoing consultations between the U.S. and South Korea indicate that the extended deterrence commitment to South Korea remains U.S. government policy.

Avoiding Content at Odds with Trump's 'America First' Policy

Some observers suggest that both the new NDS and last month's National Security Strategy (NSS) focus on strengthening U.S. dominance in the Western Hemisphere (the Americas and surrounding regions) and increasing allies' burden-sharing-key themes favored by President Trump and his supporters under the so-called "America First" approach. As a result, the extended deterrence commitment, seen as a "burden" for the U.S., was omitted.

Even considering these political factors, the decision not to explicitly mention the extended deterrence pledge in the highest-level defense strategy document raises concerns about the message it sends to allies such as South Korea and to adversarial states. Many argue that if U.S. allies begin to doubt whether "President Trump would actually fulfill the nuclear umbrella commitment even at the risk of the U.S. mainland facing a nuclear attack from adversaries," it would ultimately be detrimental to nuclear nonproliferation. Anxiety over the reliability of the U.S. nuclear umbrella could lead to increased desires for independent nuclear armament.

Deterring China Through 'Peace Through Strength'

The NDS states that the goal regarding China, the U.S.'s main rival for global leadership, is to achieve a "decent peace"-one that is favorable to the U.S. but also acceptable and coexistent with China. The core is not confrontation, but deterring China in the Indo-Pacific through strength. The strategy pursues "deterrence by denial," making it clear to China that "an attack would be futile." This means denying and preventing the adversary's attack from succeeding.

This aligns with Trump's long-held emphasis on "peace through strength." To this end, the NDS states that the U.S. will "establish a strong denial-based defense" along the First Island Chain (the primary defense line running from the southern tip of Kyushu, Japan, through Taiwan and the Philippines). As a result, it is highly likely that U.S. military posture adjustments will be made in the Indo-Pacific, such as strengthening the status of U.S. Forces Japan and increasing the flexibility of U.S. Forces Korea.