Using
this set of GDP data, and a Sharpie on the back of a wet napkin:
Iraq 2: 1.1% of GDP
Iraq 1: 1.2%
Vietnam: 2%
WW2: 56%
WW1: 16%
Span-Amer: 2%
Civil War: 22%
Beyond that I doubt the numbers are meaningful.
Well yeah, it's 1.1% that could surely have been spent more wisely.
This does indicate the difference between "war" and "total war" ala WW2 in which the fight is thought to be for one's very existence as a nation, as a culture. Pretty much the whole banana is avoiding one of those kinds of wars. Whatever we could do to avoid that would be great.