i'm convinced that we will someday have a single world currency. i'm pretty sure that this single currency won't be adopted through a smooth transition.
i kinda think the the USD may turn to confetti first.
the US has been taking on too much debt for too long and shows no sign of stopping. at every level, we overspend, national, state, city, and private budgets are all overloaded with debt. we keep inflation relatively low to make it easy to get more loans.
eventually, we may find ourselves in the position where our debts exceed our reasonable expectation of being able to pay them off. Germany faced this when they were loaded down with reparations debt after WWI. they responded in the only reasonable way: by turning their currency into confetti. and viola, their debts were gone.
i doubt the US will take such drastic measures, but i wonder if we aren't intentionally causing price inflation to help devalue some of our debts. because many of our national debts (social security, veteran's payments, treasuries) are dollar denominated or weakly adjusted for inflation (through CPI), devaluing the dollar is an effective way of reducing their real value. since a large fraction of the treasuries are held overseas, reducing their value doesn't even directly hurt americans.