And, in this war, there won't be a real victor.
"We're in the midst of an international currency war, a general weakening of currency," Mantega told The Financial Times. "This threatens us because it takes away our competitiveness."
Mantega's comments came just weeks after Japan joined Switzerland in intervening in the foreign-exchange market. But the reality is that the currency war has been under way since 2008.
At least, that's when Money Morning Chief Investment Strategist Keith Fitz-Gerald first warned that countries - most notably the United States - would debase their currencies in a race to boost their exports and keep economic growth afloat.
"The government has adopted a weak-dollar policy," Fitz-Gerald said in an interview in March 2008. "They're sending out a message loud and clear: 'We want you to sell the dollar.'"
By holding the central bank's benchmark lending rate down in a record low range of 0.00% to 0.25% for close to two years now and buying up Treasuries in a policy known as "quantitative easing," the U.S. Federal Reserve is effectively debasing the dollar.
But the U.S. central bank isn't alone.