Discussion over the future of US alliance politics in Asia has recently intensified. China’s power is growing, and US President Donald Trump is showing antipathy towards what he views as insufficient allied efforts to support America’s defence strategy in the region.

While much attention has been understandably directed towards the US’s security ties with Japan and South Korea during Trump’s ongoing efforts to negotiate a denuclearisation agreement with North Korea, US strategic relations with Southeast Asia and its neighbours—what’s termed here as the ‘southern flank’—are also critical to Washington’s own long-term geopolitical interests and to that region’s sustained economic growth and geopolitical stability.