CaliToday (23/9/2025): As the Trump administration prepares to unveil its first National Defense Strategy (NDS), a high-stakes debate is intensifying within Washington's foreign policy circles over the future role of nuclear weapons in U.S. alliances, with a particular focus on Asia. The central, once-unthinkable question being discussed is whether the United States should tolerate, or even tacitly accept, key allies like South Korea developing their own nuclear arsenals.
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| Courtesy of South Korean presidential office |
This conversation marks a potential seismic shift from decades of steadfast U.S. policy aimed at preventing the spread of nuclear weapons, even among its closest partners.
Jennifer Kavanagh, a senior fellow and director of military analysis at the think tank Defense Priorities, stated that while U.S. troop numbers in South Korea may not change immediately, the long-term trajectory could compel allies to reconsider their own nuclear options.
Speaking to South Korean media on September 15, Kavanagh noted a significant change among some Pentagon strategists who now believe that "limited nuclear proliferation among allies could be acceptable."
The 'Restraint' Doctrine and its Implications
This emerging viewpoint, according to Kavanagh, reflects the thinking of the "restrainers," an influential group of U.S. policymakers and analysts who advocate against expansive overseas commitments. Among them is Elbridge Colby, the Under Secretary of Defense for Policy, who is leading the drafting of the NDS. Their perspective posits that if the U.S. forward-deployed presence is reduced, Washington should be open to its allies developing their own deterrent capabilities to fill the security gap.
"As the world changes, treaties must be reconsidered," Kavanagh said, explaining the principle that underpins the willingness of some in Washington to tolerate a nuclear capability for trusted allies like South Korea or Japan should U.S. commitments wane.
This possibility arises amid persistent questions about the sustainability of U.S. security guarantees. President Trump has long urged allies to increase their defense spending and contribute more directly to their own defense. Critics argue that if U.S. forces withdraw or reduce their role, Seoul could face immense pressure to pursue an independent nuclear arsenal to counter the growing threat from North Korea.
High Stakes for the Indo-Pacific
Concerns about a South Korean nuclear path have surfaced repeatedly within Seoul's policy circles, driven by North Korea's relentless development of missiles and nuclear warheads. For Washington, even a tacit acceptance of an ally going nuclear would mark a profound strategic shift. Such a move could:
Undermine the Nuclear Non-Proliferation Treaty (NPT): Potentially triggering a domino effect of nuclear development in Asia, with Japan and even Taiwan reassessing their defense strategies.
Complicate Relations with China and Russia: Both nuclear powers are vehemently opposed to the emergence of new nuclear states in the region.
Proponents of this more flexible approach argue that allowing allies to develop nuclear weapons could reduce the burden on U.S. forces while still ensuring effective deterrence. They point to Poland and other European allies seeking stronger security guarantees, arguing that if the U.S. is unwilling to respond directly to incidents like intruding Russian drones, allies must assume greater responsibility.
Opponents warn that tolerating new nuclear powers could destabilize alliances and spark regional arms races, creating a more dangerous and unpredictable world.
The new NDS, currently circulating in draft form at the Pentagon, is expected to prioritize China as the U.S. "pacing threat." However, the introduction of nuclear policy into discussions about force posture in Asia suggests the administration may be leaving the question of allied deterrence open.
Kavanagh's remarks highlight the risks facing U.S. allies. While she suggested that the short-term military presence in South Korea would likely remain stable, she warned that over the next decade, Washington may reduce its permanent footprint. If that happens, she concluded, "investment in independent defense, including nuclear options, may be the only path to ensure sovereignty."
