Question

What might cause a change in the value of fiat money

Answer 1

The value of fiat money is determined by the supply and demand. It is not supported by a commodity like gold or silver but rather on how much trust is put on it. If the people begin to doubt the currency then it will lose its value.

Answer 2

I believe the answer is: a change in government regulations

Fiat money refers to the type of currency that usually do not have intrinsic value, but would suddenly have a value after a certain legislation.

For example, your $ 100 bill does not made from a material that is worth $ 100 in value (unlike gold coin. your dollar bill was made from paper)
But it suddenly have value after the government regulation mandated that it is worth $100 for exchange.