“We’re in the midst of an international currency war, a general weakening of currency. This threatens us because it takes away our competitiveness.” This complaint by Guido Mantega, Brazil’s finance minister, is entirely understandable. In an era of deficient demand, issuers of reserve currencies adopt monetary expansion and non-issuers respond with currency intervention. Those, like Brazil, who are not among the former and prefer not to copy the latter, find their currencies soaring. They fear the results.

This is not the first time for such currency conflicts.?In September 1985, now 25 years ago, the governments of France, West Germany, Japan, the US and the UK met at the Plaza Hotel in New York and agreed to push for depreciation of the US dollar. Earlier still, in August 1971, the US president Richard Nixon imposed the “Nixon shock”, imposing a 10 per cent import surcharge and ending dollar convertibility into gold. Both events reflected the US desire to depreciate the dollar. It has the same desire today. But this time is different: the focus of attention is not a compliant ally, such as Japan, but the world’s next superpower: China. When such elephants fight, bystanders are likely to be trampled.

Here there are three facts, relevant to today’s currency wars.