The Fed’s planned purchases of $600 billion of long-term Treasury bonds were targeted for domestic problems, but are having international consequences. The expansion of the Fed’s balance sheet drives down the foreign-exchange value of the U.S. dollar, and (same thing) forces other currencies to appreciate in value.

Emerging markets with high short-term interest rates will attract “hot money” flows. These flows are not stable sources of funding, and disrupt the small capital markets in these countries. Long-term, the appreciation of their currencies harms their competitiveness in global goods’ markets.

Brazil has already imposed capital controls and other emerging markets may follow. The Chinese in particular have reacted sharply. According to a Reuters dispatch, Xia Bin, adviser to China’s central bank, said another financial crisis is “inevitable.” He added that China will act in its own interests.

In short, the Fed’s actions have undone whatever good came out of the G20 meetings. Any hope for cooperation on currency values and financial stability is out the window. There are potential spillovers in other areas of global cooperation.

Currency wars, like other wars, have unintended consequences and collateral damage. Some countries will predictably react by imposing capital controls. Moves to curb imports can follow. Monetary protectionism leads to trade protectionism.

However it might like matters to be, the Fed cannot simply act domestically. It has reached the useful limits of further easing.