It’s less than a week since Donald Trump’s sensational announcement that he was unilaterally ending the world’s trading system with the imposition of a 10% minimum tariff for trading with the US – and a very much higher rate for those countries unfortunate enough to have the US as a major export partner. Long-term allies such as Japan and South Korea have been hammered with tariffs of around 25%, while export-dependent poorer countries such as Vietnam, which sells about a...