The value of a currency eventually leads back to the government that issued it. When I spend a Dollar, the business that gets it puts it in a bank account. Tha

The value of a currency eventually leads back to the government that issued it. When I spend a Dollar, the business that gets it puts it in a bank account. That Dollar can (theoretically) be taken to the issuing bank, in this case the Fed, by the business' bank, in order to get something of value. To enforce the trading of Yuan, the Chinese we do not value Yuan held by in foreign accounts (or in the case of the "international" Yuan, it's value is restricted). So now those pieces of paper you have with Chinese lettering (or that account valued in Yuan) has nobody that gives it value... it's worthless.