The problem is that the policy has also caused the yen to depreciate, leading nearby countries to accuse Japan of adopting “beggar-thy-neighbor” policies. Similarly, emerging-market officials warned that monetary expansion in the US and the UK would trigger a wave of competitive currency devaluations, with Brazilian Finance Minister Guido Mantega going so far as to accuse the Fed and the Bank of England of waging a full-blown “currency war.”