NEW YORK (CNN/Money) - When you think of it, America has become everybody's central banker.

Take China, for instance. Sure, the People's Bank of China does central banker things like setting reserve requirements at banks, but its main job lately seems to be keeping China's yuan pegged to the greenback.

What dollars come to the country -- either from exports or direct investment -- have to either be banked (why China's Treasury holdings are growing) or bought with yuan. Plenty of the latter is going on, to judge from the rapid growth in China's money supply. (China's M2 expanded at 19.6 percent in December.)

A similar dynamic occurs within other economies that have dollar pegs, such as Hong Kong and Malaysia.

Then there's Japan, which doesn't have a peg per se, but has taken great pains to keep the yen from appreciating too much against the dollar. So far in January, Japan's Ministry of Finance is believed to have sold ¥6 trillion (which comes to around $55 billion) for greenbacks. That's a monthly record and comes to something like a quarter of all of last year's dollar buying.

Finally, there's Europe, where officials have been grumbling ever louder (to some effect) about how the euro's strength could sap the economic recovery. There has been some talk among forex traders about the possibility that the European Central Bank might intervene in the currency market to stem the euro's strength. The more likely course of action is a cut in interest rates, which a growing number of observers have come to expect, paired with pressure on Asian economies to let their currencies strengthen.

Why is it that all these currencies, left to their own devices, would likely strengthen against the dollar? It undoubtedly has something to do with the U.S. current account and budget deficits, something to do with the belief that other places are going to offer hotter returns on your investment than America right now.

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But it also has something to do with supply. Washington passed a big fiscal stimulus package last year which still hasn't worked its way entirely through the system. More important, the Fed has brought the fed funds rate to a 40-year low and has given no indication that it's going to lift it anytime soon. Certainly not at its meeting this week.

It's an incredibly inflationary monetary policy, one that seeks to put as many dollars in the economy as possible. Other countries, loathe to see their currencies rise too much, have taken to printing enough money to absorb this supply. The result is that they've ended up with the same easy-money policy as the United States. Whether that policy is really what their economies need is an open question.