The fundamental problem you’re going to have is that any point you decide is the beginning of debt based fiat currency, well there’s still a crap ton of war before it. If you say that the brits were really using fiat during WW1, a dubious argument, then I’m going to gleefully point out that the Romans conquered the Mediterranean using physical gold & silver coins; no fiat.

It’s entirely possible to fund massive wars without fiat currencies. We know this because we’ve seen it time and again. Taxes and bonds can be used even with a hard metal currency, as does the handy expedient of promising a portion of the spoils of war. I see no reason why a bitcoin based country couldn’t just raise taxes and bonds just like the gold backed ones did for literally all of human history.

Beyond that, the world hasn’t seen any truly massive multi-lateral engagements since the proliferation of fiat currency. While the Middle East remains a hot spot, there has been nothing to match the scale and hardship of a world war or a napoleonic war. If the theory is that fiat currency enables war, you’re going to have a very hard time explaining the limited scope of conflict since the abandonment of Bretton Woods in 1971.