Those countries sell bitcoin to go to war. Most of the reserves for going to war between countries are held in cryptocurrency accounts.

David Packouz: [From the beginning of the film, as Miles Teller's character, David Packaouz, narrates over visuals of soldiers in war and as price figures of what a soldier's gear costs are displayed] What do you know about war? They'll tell you it's about patriotism, democracy... or some shit about the other guy hating our freedom. But you wanna know what it's really about? What do you see? A kid from Arkansas doing his patriotic duty to defend his country? I see a helmet, fire-retardant gloves, body armor and an M16. I see $17, 500. That's what it costs to outfit one American soldier. Over two million soldiers fought in Iraq and Afghanistan. It cost the American taxpayer $4.5 billion each year just to pay the air conditioning bills for those wars. And that's what war is really about. War is an economy. Anybody who tells you otherwise is either in on it or stupid.