Chapter 1: US Strategic Restraint and Japan’s Security

The US’s inward shift

Leveraging the 250th anniversary of the Declaration of Independence in 2026, President Donald Trump will likely attempt to maintain political momentum by doubling down on “America First” policies. However, high tariffs and crackdowns on illegal immigration have worsened employment conditions and intensified inflationary pressures. The delayed release of documents regarding the late sex offender Jeffrey Epstein has also created political headwinds for the president. If Democrats win a majority in the House in the 2026 midterm elections, impeachment proceedings against President Trump may be considered. For the time being, US domestic politics will remain unstable, making an inward-looking orientation unavoidable.

The decline of “prioritizers” and the rise of “restrainers”

While President Trump advocates “peace through strength,” his administration’s National Security Strategy marks a retreat from the first term’s “prioritization” (prioritizing the deterrence of China). In its place, “strategic restraint” aimed at avoiding excessive overseas intervention has come to the forefront, prioritizing the security of the US homeland and the Western Hemisphere (the Americas) while making engagement in Europe and the Middle East selective.

Conversely, the administration has shown a willingness since the summer of 2025 to use military force against Venezuela under the guise of stopping drug trafficking. This signals a return to the Monroe Doctrine and an active interventionist stance within the Western Hemisphere. Furthermore, the June 2025 airstrike on Iranian nuclear facilities demonstrates that the US will still employ limited, targeted force outside of the Western Hemisphere.

In Asia, the strategy advocates for maintaining a deterrent posture against China but asserts that the US cannot – and should not – maintain the military balance alone. Consequently, it strongly demands that allies strengthen their self-defense capabilities along the First Island Chain and expand support for US forces. Defense Secretary Pete Hegseth has categorized allies as either “partners” or “dependents” based on their defense spending, suggesting that the US might abandon any defense obligations to “dependent” nations. Meanwhile, with President Trump making mention of a “US-China G2,” the National Security Strategy emphasizes reciprocal economic relations with China. From the perspective of restrainers, the US commitment to defending Taiwan may further recede in the future.

Outlook for nuclear deterrence

President Trump is expected to maintain a powerful nuclear force. As China rapidly expands its nuclear capabilities, though, the focus will be on whether the US possesses the will and capacity to maintain a nuclear balance with both China and Russia. While Trump has previously called for arms control with both nations, his administration also plans to build new battleships as part of a “Golden Fleet” equipped with sea-launched nuclear cruise missiles, suggesting an increase in non-strategic nuclear weapons. Future attention must be paid to how upcoming Nuclear Posture Reviews balance nuclear deterrence with arms control.

The Trump administration’s National Security Strategy notably makes no mention of North Korean denuclearization. Since engaging in talks during his first term, Trump has repeatedly expressed interest in resuming negotiations with North Korea. Given that North Korea rejects negotiations predicated on denuclearization, there are concerns that Trump may officially recognize North Korea as a nuclear-armed state and pursue arms control negotiations instead.

Impacts on the Japan-US Alliance

As strategic restraint becomes mainstream in the US, Japan will be required to play a larger role within the alliance. First, Japan will likely face demands to increase defense spending to 3.5% of its GDP. Japan will then have to determine whether to meet this demand, how to secure funding, and where to strengthen its defense posture amidst a declining birthrate.

Second, there is a risk that the US and China may begin to recognize each other’s spheres of influence as the Trump administration prioritizes the Western Hemisphere. A US-China G2 scenario
–    where the US withdraws from Asian affairs in exchange for China exiting the Western Hemisphere
–    cannot be ruled out. If such an agreement is reached, the likelihood of Taiwan being absorbed by China increases, forcing Japan to re-evaluate its security policy currently centered on the Japan-US alliance.

Most importantly, the US may cease to uphold a rules-based international order, with power politics replacing the rule of law as the basis for international relations. Growing US skepticism toward alliances will also pressure Japan to build a more autonomous defense capability. Even if internationalism regains momentum in the US in several years, returning to liberal international relations will not be easy.

Recommendations

To avoid the “worst-case scenario” of a US-China G2 and the revival of power politics, Japan should take the following actions:

• Normalize high-level diplomacy: In the Trump administration, policy is shaped by the president and a small circle of cabinet members or advisors. To influence policy, frequent high-level diplomacy by the prime minister and cabinet members is essential. In addition to “2+2” meetings, ministerial-level talks on extended deterrence should be held as needed.
• Strengthen self-defense capabilities: As the US demands increased defense spending, Japan must consider its own requirements regarding missiles, aerial/underwater drones, submarines, integrated air and missile defense (IAMD), and operations in cyber, electronic, and space domains.
  Regarding the defense industrial base, closer Japan-US cooperation in shipbuilding and advanced technology development is required.
• Establishing island chain defenses: Assuming scenarios of armed attack or existential threats, Japan should promote cooperation with the US for the defense of the First and Second Island Chains, as well as the sea lines of communication (SLOC) connecting them.
• Build multilateral security frameworks: To reduce the relative burden on the US military while maintaining its engagement in the Indo-Pacific, Japan should aim to expand existing frameworks like the Japan-US-Australia-Philippines “Squad”. This involves inviting nations such as South Korea, the UK, France, and Germany to create a broader, flexible multilateral security framework.

(December 31, 2025)

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