Caused by when a currency (money) becomes worthless...The value of money is always certain ellal because its a virtual entity i.e. it can be made to represent whatever we like.
Today's commodities are oil, gold, precious metals and stones etc ... If they run out or everyone has too much of them we simply make the value something else ... Something that the US has most of
MW
Tell that to the Germans in the 30s. A barrow load of dosh for a loaf of bread.
It's called hyperinflation.
And not surprising that when the debts of the US are called in, they'll quite happily pay in dollars - because they have a backup currency (the amero) waiting!
Exactly the same as going bankrupt and starting all over again - only on a countrywide scale!