Extended Nuclear Deterrence Under Strain: New Security Dilemmas
Trust in the US extended nuclear deterrence system is eroding, prompting South Korea, Poland, and the Baltic states to explore independent security guarantees. Researchers Jennifer Lind and Daryl Press from Dartmouth College examine the drivers behind this shift—particularly Russia's 2022 full-scale invasion of Ukraine and policies under the Trump administration. They outline options for Seoul, including a NATO-style nuclear-sharing agreement or withdrawal from the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) to develop an indigenous arsenal. For NATO, they propose reforming the alliance's nuclear-sharing program by moving from a single-decision mechanism to a three-key system.
Why the Umbrella Is Cracking
The US extended deterrence framework dates back to the Cold War. In 1961, French President Charles de Gaulle famously questioned whether Washington would risk New York to defend Paris. At that time, the US stationed troops and tactical nuclear weapons along the borders of West and East Germany, as well as on the Korean Peninsula. However, Russia's 2022 invasion of Ukraine served as a stark wake-up call, forcing allied nations to reassess their reliance on American nuclear guarantees.
South Korea, already equipped with ballistic missile submarines, advanced aviation, and mobile ground-based missile systems, is poised to act independently. Washington has agreed to support Seoul's development of nuclear-powered submarines using low-enriched uranium, further bolstering its defense capabilities. Researchers present two pathways for Seoul:
- a nuclear-sharing agreement modeled after NATO's program,
- a full withdrawal from the NPT to pursue an independent nuclear arsenal.
In Europe, Poland and the Baltic states have shown the strongest interest in a new US plan to station nuclear deterrence assets on the continent. However, Poland lacks both submarines and sufficient nuclear fuel stockpiles. Under NATO's current nuclear-sharing arrangement, the US president retains sole authority over weapon use. The proposed reform would shift from a one-key to a three-key system, potentially reshaping the region's security architecture.
This growing crisis highlights an urgent need among nations once dependent on the US nuclear umbrella to develop their own security mechanisms. Russia's invasion of Ukraine has acted as a catalyst, compelling regional powers to seek independent paths to ensure their defense. The outcome could lead to novel forms of security cooperation and a fundamental shift in the global balance of power.
The shifting dynamics of NATO's nuclear strategy are further highlighted by recent developments, such as the US's decision to block the sale of Tomahawk missiles to Germany, reflecting heightened concerns over Russian aggression. This move underscores the growing anxiety among European allies regarding their security and the reliability of American commitments, prompting nations like Germany to reconsider their defense strategies in the current geopolitical climate.