war is primarily funded by inflation. bitcoin doesn't have inflation (it's lower than gold). the roman empire funded their wars in the late days by diluting the gold, copper and silver coins with tin. the oldest recorded example of this kind of government war funding was in Egypt with Joseph, who essentially established the first central banking regime, and this led to 7 years of famine, and plagues.

the primary way that wars are funded is by debasing the money, because people don't notice it straight away.