Incidently, you should read up on what happened in Great Britian in the 70's when their currency collapsed. The world currencies are really a basket of currencies from various nations. Those in the basket get to print their own money. That gets into a more complicated scenario with values, QE, and trade and a host of other topics.
Given our situation of 17 trillion in debt and over 90 trillion in unfunded liability, which nobody talks about either, how do you think America's book will end ? Some will certainly blame capitalism, but I say to you it will be not from the capitalism theory, but those who's hands it's success or failure was placed in.