"Obviously, all currencies cannot depreciate at the same time. Currency war is like a "zero-sum game": a situation in which each country's gain (or loss) is exactly balanced by the other countries losses (or gains). For instance, due to the Fed's QE in 2008-2012, on one hand, the US economy has recovered (i.e. stronger labour markets, more job creations or lower unemployment, wage recovery, etc.) but, on the other hand, this policy led to high inflation, currency appreciation, lower of export competitiveness, and spike in asset prices in emerging markets."