Bangladesh, Sept. 25 -- The Pentagons ongoing review of the United States military presence in Europe could become one of the most consequential defense-policy decisions of the Trump administration. Although the review is focused on Europe, its implications are likely to extend well beyond the continent. The decisions made in Washington could affect NATOs future, Americas ability to respond to crises in the Middle East, its military posture in Asia, and the broader relationship between the United States and its allies.

For decades, American forces have served as a central component of Europes security architecture. The size of the US military presence has declined significantly since the Cold War, when hundreds of thousands of American t...