Any “prosperity” that a nation enjoys while in wide armed conflict with another nation, only comes at a fearsome cost in lives and the salvage of a great deal of real wealth taken as spoils from other combatants.
As an example, the large amount of war materials sent to England in 1939 and 1940 and 1941, was being paid for by the English in silver bullion, which was being shipped back to the US on the back haul from delivering the ammunition, armored vehicles, and fuel supplies to England. FDR was not doing this out of the goodness of his heart, it was highly remunerative for the US economy. The English, on the other hand, were spending themselves broke fighting off the Nazi attacks, and they were scarcely better off than the US from the effects of the world wide depression that seemed to grip everywhere. The Nazis, of course, so long as the fighting was not on their own soil, were robbing all the wealth from the nations they had occupied, and in the early years of WW II, the civilian population there enjoyed enormous prosperity.
Of course, the situation reversed as the war went on, and the real costs of making war came back to bite just about everybody in the butt. Big time. The purpose of war is to make noise, kill people and break things. Not to “improve” the economy or “increase” prosperity.
Build expensive stuff, ship it halfway around the world and then blow it up.
The obvious route to prosperity.
That said, WWII absolutely eliminated unemployment in USA.
And therein lies the trouble with economists that are in love with their tools - i.e., statistics and time series. They don't take the time to look beyond the numbers to get a sense of what those numbers stand for. In a nutshell, a tank is not a ranch house; nor is it a Cat.
There's another trouble. The "World War 2 got us out" argument relies upon patriotism, which makes it hard to question. We're already inclined to believe it because it jibes with World War 2 as a great renewal capstoned by the unconditional surrender of Fascist Italy, Nazi Germany and Imperial Japan. One form of totalitarianism was vanquished: what else but good could result from the good fight?
The trouble with such grand narratives is that they turn into misleading myths long after the fact. The kind of myths that can lead to real trouble down the road.
In the broader sense, scholars like Higgs are the civvie answer to the WWII vets who published post-war tell-alls showing that war was indeed hell. They tell unconfortable truths, true, but they're necessary for subsequent decision-making.