With Fiat currency, governments can finance wars through; money creation, sovereign debt and inflation, just to mention a few, in most cases such measures delays the political consequences of war.
Before fiat creation, there were wars, both within countries because of internal conflicts or political reasoning and also there were wars between countries. I mean not just wars, but numerous wars.
Fiat is not the reason war is existing. Also bitcoin can not end war because people have the mindset of waging war against each other.
I think the reason you posted this is what you have heard about the dollar dominance which United States used to have dominate power and the country was in war with Iran recently.