not with an international market that would have already devalued the fiat countries economy. the war would be over before it even started. 

Ok, but "overnight" is still enough time to finalize a contract for munitions and supplies.

Lets say the money supply doubled just now. The market doesn't even have a chance to price that until that new money is spent at least once.

nullcount

Devaluation can happen overnight. Market is smarter now. 
Unless you are the world reserve currency. Then you have a bit more time. But the ultimate result is the same. 

quark

bitcoin

Wars between countries with Fiat vs Bitcoin?

HardRich

True, but it takes time for this devaluation to be priced by markets. This is why we have cantillionaires who spend the new money while the market thinks its still worth something.