At best, a very accurate simulation could tell you "in the case of war, here is the expected distribution of outcomes, here are the probabilities of various levels of "winning", here are the estimated levels of civilian casualties.
And quite a few political leaders in such situations have or would have chosen to take e.g. a 5% chance of victory instead of surrender, or simply as a deterring tactic - yes, we know that we will surely lose, but in the process you'll lose many men as well, so we'll bet that the result is not that important to you and you won't pay this price.
If Herodotus is to believed, a Persian siege against Babylon was met with the Babylonians strangling all the women except for a few to make bread as to stretch fighting resources as long as possible.
During the Sono-Soviet border conflict of the late 1960s, Mao threatened to overwhelm the Russian border with millions of Chinese as a part of his "man over weapons" strategy. Even with nuclear weapons, the Soviets were terrified of the sheer number of people that China could throw at them.
How do you predict that? How do you put a number to it?
War is always political.
I was meaning more that a conventional war is more violence then politics. There are various aspects to war, each type has its own balance of these aspects. I just feel that in a guerilla war the politics has as much a part as violence.
Now, Germany was obviously occupied on multiple fronts.
While I can't contest that if a nation of 330 million were to devote its full human and industrial capacity for the purpose of destroying all resistance in a nation of 33 million, it would succeed...
I wouldn't call the richest country in the world failing to convert to a war economy to overcome an enemy ten times smaller then they are to be 'lack of will to win.'
The richest nation in the world should not have to convert to a war economy to defeat an enemy ten times smaller. If it could not; then it didn't want to be there in the first place, it didn't want to do what was necessary to win, or their internal politics is screwed up. Possibly more than one of those.
It was clear then too, but it obvious now that the proto-ISIS "freedom fighter" narrative was completely divorced from reality.
Heck it might even prevent war if the simulation says that both sides will suffer too high casualties to make it worth it.