ED 'America First' defense posture

Elbridge Colby, U.S. under secretary of defense for policy, speaks at the Sejong Institute in Seoul, Monday. Yonhap

The United States’ call for allies to take on a more central role in defense materialized again with the release of the 2026 National Defense Strategy (NDS) by the Department of Defense Friday. The document urges allies such as South Korea to assume “primary responsibility” for their defense, with the U.S. providing "critical but more limited" support.

The shift aligns with President Lee Jae Myung’s emphasis on “self-reliant defense,” beginning with the wartime operational control (OPCON) transfer and the construction of a nuclear-powered submarine. However, language calling for Korea to assume “primary responsibility,” alongside the U.S. offering only limited support, points to higher costs for Seoul and a possible reorientation — or “strategic flexibility” — in the scale and scope of operations of the roughly 28,500 U.S. Forces Korea (USFK) personnel.

The emphasis on “strategic flexibility” has heightened the possibility that USFK could be deployed to other parts of the Indo-Pacific.

The NDS makes clear that the decadeslong U.S. alliance with Seoul is entering a period of change. It defines an “America First” defense posture as one focused on protecting the U.S. homeland and ensuring military and commercial access to strategically important locations in the Western Hemisphere, including Greenland and the Panama Canal. Within this framework, allies such as Korea are expected to shoulder primary responsibility for conventional deterrence.

Elbridge Colby, U.S. under secretary of defense for policy and one of the main architects of the “America First” defense posture, met with top Seoul officials to expand on the NDS. Ahead of the meeting, Colby posted on social media upholding South Korea as a "model ally" — a stance that places added pressure on Seoul. Colby told reporters he looked forward to future discussions on "modernizing and advancing the alliance."

A disconcerting aspect of the NDS for Seoul is that, like the State Department’s National Security Strategy released last month, it omits references to a commitment to North Korea’s denuclearization. Seoul has pursued engagement with Pyongyang while maintaining its adherence to the North’s denuclearization, albeit with a more pragmatic and flexible approach. One such approach is Lee’s three-step, phased plan of freezing, reducing and dismantling North Korea’s nuclear and missile programs. “It would be beneficial if no additional nuclear material is produced, if such material is not transferred abroad and if ICBM technology is no longer developed,” Lee has said.

Seoul will need to persuade Washington in future talks to acknowledge its pragmatic approach, while encouraging its alliance partner to back an engagement-based path toward denuclearization.

Another concern is that the NDS makes no reference to “extended deterrence.” Experts are split, with some interpreting the pledge of “critical” U.S. support as encompassing the nuclear umbrella, while others say the omission is significant. This is despite the NDS itself warning that North Korea’s nuclear forces are increasingly capable of threatening the U.S. homeland and are "growing in size and sophistication, and they present a clear and present danger of nuclear attack" on the U.S. homeland. Although the forthcoming U.S. Nuclear Posture Review may provide guidance, Seoul should use future defense dialogues to seek clearer assurances on extended deterrence and the nuclear umbrella.

Moreover, both sides should reaffirm that denuclearization remains the overarching goal, should dialogue resume between the United States and North Korea.

President Lee has stressed on social media that “in an unstable security environment, self-reliant national defense is fundamental,” adding that South Korea — which spends about 1.4 times as much on defense as North Korea’s entire GDP and has the world’s fifth-largest military — must be able to defend itself. The president must reassess the state of the military, shaken by the martial law declaration of Dec. 3, 2024, as he moves to turn his pledge of self-reliant defense into concrete action.