See:
There Is No Escaping History. Fiat Currency Eventually Fails.
Notice that this is a critique of fiat money -- not a critique of state-issued money under a gold/silver or other standard. Fiat money is a rare occurrence in modern history. (We live in strange times!) As we can see, the examples found by the author are a small number of short periods here and there.
I have my own critique of gold/silver standards, but that's another issue.
Any particular fiat currency can fail, and there is a long track record of failure, but fiat currency as a concept is actually just fine, and in fact the most useful way to sort out trade, because it is simply too inefficient to go back to a pure bartering system. On the other hand, technology is deflationary, the cost of goods and services goes down with respect to the total amount of money in the system.
Countries got out of the depression in the exact order in which they left the gold standard. A growing economy needs an ever growing stock of money for transactions.
Yes, this is how matters stand with fiat vs. so-called hard currencies backed up by gold, silver, or any other tangible asset. But it is hard for many or even most people to understand that as they see the value of their money being constantly eaten away by inflation. In the majority of countries around the world annual inflation is two digits anyway, and in some like Venezuela it is outright ruinous. But it is not the fault of fiat money conceptually, it is rather the failure of the government that runs that currency. It is like a potent drug which can save your life but it can also lead to devastating consequences if misused or abused.