When the United States declared China a currency manipulator on Monday, long-building trade tensions between the world’s two largest economies spread to the combustible realm of currencies — with potentially huge consequences for the global financial system should the escalation continue. Did China allow the value of the yuan to fall against the dollar simply to allow it to better match the nation’s economic situation, as the country’s leaders and many international economists argue? Or was it, as President Trump contends, an effort to give Chinese exporters an unfair advantage in trade? That clash reflects Mr. ... (full story)