The Fed has always wanted to launch a third round of quantitative and loose monetary policy, also known as QE3, to boost the recovery of the US economy. If the Fed launches QE3, the global supply of dollars will increase sharply again, and countries will have to buy dollar assets in order to maintain exchange rate stability. If countries buy dollar assets, it will increase inflationary pressure in their own countries. If you don't want to import inflation, countries have to let their currencies appreciate. If the local currency appreciates, it will depress domestic exports and lead to an economic downturn.
If other countries do not experience imported inflationary pressures, they will not let their currencies appreciate if the above statement is true.