Imagine a battlefield where, after repeated fighting over 15 years, the various sides have declared an armistice and a fragile peace reigns. Combatants are keen not to start hostilities again: indeed, one of the main actors is incurring considerable expense to avoid any appearance of belligerence. Then, out of the blue, one of the armies, led by a new and untested general, marches into the middle of the combat zone and declares war on a number of fronts.

This describes the arena for the currency wars, one of the main theatres of conflict in international economic diplomacy. During the early 2000s, and then again in the years following the global financial crisis, the US repeatedly accused other countries of deliberately undervaluing their exchange rates to gain a competitive advantage.

This week Donald Trump’s administration have identified China, Japan and Germany as hostile forces in this regard and promised to take them on.