The US has promised to usher in a “new era” in relations with its most important allies in Asia, as the region struggles to address the threat posed by an increasingly assertive China and a nuclear-armed North Korea. Joe Biden is expected to take advantage of a recent thaw in ties between Japan and South Korea – home to tens of thousands of US troops – to announce new collaborations on missile defence and technology, when he meets the countries’ leaders on Friday. Biden will host the South Korean president, Yoon Suk Yeol, and the Japanese prime minister, Fumio Kishida,...