Trump’s South Korea defense move puts Japan’s 75-year security plan at risk

WASHINGTON, 23 AUGUST 2026 —

TOKYO — Donald Trump’s call to cut joint US military exercises with South Korea has exposed the fragility of Japan’s long-standing security strategy, analysts and officials say.

The US president’s social media post on Monday, which proposed scaling back drills “based on my very good relationship with Kim Jong Un,” removes one of the pillars underpinning Japan’s postwar pacifist constitution without offering any replacement. For 75 years, Tokyo has relied on Washington’s military guarantee under the 1951 security alliance, leaving little room for alternative defence planning.

“This is the sharpest stress test the alliance has faced since the Cold War,” said a defence analyst quoted by the Financial Times. The comment underscores how quickly strategic assumptions can shift when US commitments appear less predictable.

Japan has begun moving toward a contingency plan, but remains far from a viable alternative. An annual defence white paper published this month pledged that by fiscal 2027 the country would develop the capability to take “primary responsibility” for repelling an invasion, though still with US support. Defence analysts describe this as incremental progress, not a true Plan B.

Prime Minister Sanae Takaichi faces competing pressures. Weekly protests outside her residence demand she uphold pacifism, while opposition voices and regional tensions push for a harder security stance. China has labelled her a militarisation hard-liner, North Korea has escalated anti-Japanese rhetoric, and Russia’s president Vladimir Putin visited one of four disputed islands near Hokkaido last week.

Tokyo has tried to reduce its exposure to US unreliability by expediting a US$550 billion pledge to invest in the US and positioning itself as a critical link in American supply chains and defence production. Yet Trump’s willingness to decouple regional security from long-standing US interests—juxtaposing the Korea drill cuts with a reminder that South Korea had not joined America’s campaign against Iran—signals a deeper rupture in Washington’s strategic calculus.

For Malaysian business readers, the episode shows how sudden shifts in great-power alliances can ripple through supply chains and capital flows. Japan’s manufacturing networks span Southeast Asia, and prolonged uncertainty about its defence readiness could prompt companies to reassess regional exposure or accelerate moves to diversify production bases.

Related: Washington