From 'Defending the Homeland' to Global Deterrence: A New Paradigm of Geopolitical Security Under the Reshaping of US Missile Defense Strategy

In the post-Cold War era, the United States' national security strategy is undergoing a profound paradigm shift, with its core issues no longer limited to traditional area defense but being redefined by complex geopolitical structures. Documents proposed by the US Department of Defense, such as the 'National Defense Strategy' (NDS), clearly outline this transformation: on one hand, the nation is committed to countering various military threats; on the other, the focus of defense policy has expanded from traditional ground, air, and sea defense to addressing increasingly complex and volatile long-range missile threats. This strategic reshaping is essentially a systemic adjustment to the global security environment—especially in the context of intensifying geopolitical competition.

The core challenge for the US in the missile defense system currently is the need to simultaneously address two intertwined threat lines: first, the growing ballistic missile (ICBM) capabilities of North Korea, which requires the US to adopt a 'comprehensive missile defense' approach to maintain its leading position; and second, the need to deter missile threats from Russia and China, which may involve limited nuclear use.

This dual pressure forces a fundamental change in the logic of US security policy. In the past, the focus might have been on nuclear deterrence to counter large-scale conflicts, but the new security calculus requires the US to find a delicate balance between 'strategic deterrence' and 'domestic defense'. Analysis suggests that increasing the number of ground-based intercept systems (GBI) to counter the North Korean threat may create new tensions with geopolitical stability, particularly concerning relations with Russia and China. Some studies suggest that in a resource-constrained environment, over-investing in countering a single threat might inadvertently weaken strategic reliance on a broader alliance system, leading allies to question the sustainability of the US's security commitments to them.

A more structural challenge is the 'dual-nuclear power problem'. The deterrence strategies pursued by Russia and China allow them to use limited nuclear or conventional weapons to coerce the US. This compels the US to re-evaluate the survivability of its nuclear arsenal. Experts point out that the US needs to develop an 'integrated air and missile defense' (IAMD) capability to effectively counter the coercive attacks from these two powers. This is not just a technical upgrade but a restructuring of the deterrence logic—by enhancing the survivability of US nuclear forces, the cost of any potential first strike is increased, thereby complicating the opponent's strategic planning.

Furthermore, protecting its nuclear arsenal requires shifting from a traditional comprehensive defense to a 'layered defense' strategy. This means deploying missile defense systems with priority for US nuclear forces, aiming to enhance their resilience in scenarios involving limited nuclear exchanges. This 'priority defense' strategy is not intended to protect civilians but to complicate the opponent's attack paths through technical means, thereby increasing overall deterrence effectiveness.

From the perspective of international cooperation and global governance, the US's strategic adjustments in missile defense reflect the structural changes in the global security governance system.From the perspective of international cooperation and global governance, the United States' strategic adjustments in missile defense reflect structural changes in the global security governance system. When the security calculus between great powers shifts from a purely military competition to one involving 'deterrent coercion' that includes limited nuclear use, the traditional stability model based on Mutually Assured Destruction (MAD) is being tested. This demands that the focus of international cooperation must shift from a mere military technology competition to how to build a more resilient governance framework capable of managing the risk of 'limited conflicts' between great powers. For countries that rely on alliance systems, the adjustments the US makes to its domestic defense strategy directly affect its reliability status within the international security architecture.

Ultimately, the evolution of US missile defense strategy profoundly reveals a long-term trend in global development and security: in a highly competitive geopolitical environment, the effectiveness of technological defense increasingly depends on the integration of deeper strategic deterrence theories. The future security landscape will no longer be a contest between single military powers, but a complex system where multi-layered defense systems, deterrence logic, and international relations dynamics are mutually coupled. This requires policymakers and international cooperation bodies to look beyond short-term technical indicators and focus on building a globally resilient security governance framework capable of adapting to persistent, multi-dimensional threats.