Right now the only reason that central banks continue to purchase US debt (thus keeping the dollar from completely tanking) is to protect their existing investment in US dollars. But to me that just seems like throwing good money after bad money, and it will subside.

The entire US economy has become based on deficit spending as opposed to productivity, equal trade and fiscal responsibility. And macro economics are not that much different than personal economics. If you stop working, run up some personal debt, continue to run additional debt in order to pay your existing debts, continue an exorbitant lifestyle (e.g., financing stupid and pointless wars) and still fail to work and produce to support it all, what happens? You'll go bankrupt, lose all of your assets and have nothing.

The US has masked and delayed the effects of this simple truth by setting policies to get banks to pump trillions into bad loans to consumers. This has artificially inflated the housing market, which for a while attracted some foreign investment and got consumers to take advantage of the equity and sustain consumer spending. But that was all very artificial, and now we see what is happening to the housing market (and thus the economy). Thank you, Alan Greenspan.

The currency of a nation ultimately represents what that nation has…the value of its assets. And because of horribly unsound economic policies (i.e. both parties, but especially the republicans and the war criminal Bush), the US is running out of assets and no longer produces goods that the rest of the world wants. There is still some value in natural resources, intellectual capital (although that is also dissipating), etc., but I think the trend is clear.