Gold *was* money initially.  The original FRN note promised to pay gold "on demand".  Then they "outlawed" owning gold in 1933 (a bank bailout essentially making it illegal to cash your promise) and in 197? they stopped redeeming FRN for gold for foreign central banks.   So yes, the *system* defaulted on promised gold.

We are left with FRNs which are in demand because people had debts and taxes to pay.  But the fundamental scam is still growing until it all crashes in hyperinflation.