Border flare-ups between Thailand and Cambodia seem endless: Can Asean do something?

Renewed hostilities between Thailand and Cambodia are a wake-up call for Southeast Asia about the costs of letting historical border disputes fester. The century-old conflict, rooted in colonial-era cartography, is flaring at a time when the region is already straining from US President Donald Trump’s trade war and intensifying rivalry between the US and China.Fighting erupted last week along their shared frontier and so far has killed at least 11 people.

Both sides have exchanged artillery fire and Thailand carried out air strikes with F-16 jets after accusing Cambodia of firing rockets into civilian areas.The neighbours have clashed repeatedly before, most recently in July, when dozens were killed and tens of thousands displaced. A fragile ceasefire—brokered in part with Trump’s self-touted involvement—has collapsed, and there is no clear diplomatic off-ramp in sight.

Washington is concerned by the continued clashes and casualties along parts of the 800km border. US secretary of state Marco Rubio urged both sides to immediately cease hostilities and to return to the measures outlined on 26 October in the Kuala Lumpur Peace Accords, which were one of Trump’s more prominent successes in branding himself a global peacemaker.But a return to calm looks unlikely, at least in the near term.

Both governments are leaning on deeply rooted nationalist sentiment to shore up support. The hardened rhetoric lays the groundwork for a prolonged and destructive conflict.Like many disputes in Asia, this one is a hangover from Western imperialism, though the roots go back further.