South-east Asia has long lived under the shadow of an accidental war. The region's military planners prepare for mishaps or miscalculations - one sparked perhaps by an overconfident naval commander, and triggering a confrontation in the Asia-Pacific, which is the most militarised stretch of ocean anywhere on earth. The ominous shadow has lengthened with the sharpening rivalry between the United States and China.

The geostrategic fracturing was plain at the annual Shangri-La Dialogue in Singapore three months ago. The US sent out a warning against "actors" that undermine the Western-led post-World War II international order. It described the Indo-Pacific as a "priority theatre", where it deploys four times as many forces as any other combatant command. From the same stage, China deplored the destabilising effect of "outsiders". Having extensively militarised islets, reefs and shoals some 800km away from its coast, it vowed not to yield an inch on territorial disputes in the South China Sea. Their trajectories could collide.