very good topic for discussion, apologize if I leave the subject a bit. nowadays it is a question of the fact that most of the countries in which money can not be maintained are only based on an internal GDP accounting that has false sustainability (one of them being the United States which has no real support to maintain its currency afloat), the printing of currency can be given by countries to other countries or by a country to indundate with worthless bills and that can create an inflation, there are also currencies like the dollar that is maintained by the traffic of all types of materials because this currency is used worldwide for that reason does not fall into a tailspin, there are also currencies that are maintained by money laundering and falsification of them (here could name Colombia whitening pesos and dollars for the financing of drug trafficking and the falsification of dollars for the flooding of a market) could last a whole day talking about this interesting topic but it would end up being annoying for others