An annual powwow in Singapore for the Asia-Pacific security establishment, the Shangri-La Dialogue used to be interesting mainly for what went on behind closed doors. Last year however, public sparks flew between China and both America and Japan. This weekend’s dialogue may be fierier yet, as Ashton Carter, America’s defence secretary, reprimands China for its recent provocations. America’s Asian allies have been alarmed by China’s frenetic land-reclamation around disputed rocks and reefs in the South China Sea. America, to China’s anger, has sent warships and a spy-plane to the contested waters. It wants to assert its interpretation of the freedom of navigation, and to remind China that America, as Mr Carter said this week, “will remain the principal security power in the Asia-Pacific for decades to come.” China, which has just published a white paper setting out its ambition to become a bigger naval power, seems to have other ideas.