Paul Vebber, a gameplay instructor in the navy, says that in the past decade the government has started using strategy board games much more often. They do not help predict outcomes. For that, the Pentagon has forecasting software, which it feeds with data on thousands of variables such as weather and weaponry, supply lines, training and morale. The software is pretty accurate for "tight, sterile" battles, such as those involving tanks in deserts, says an intelligence official. Board games are useful in a different way. They foster the critical but creative thinking needed to win (or avoid) a complex battle or campaign, he says.
The article goes on to explain that board games are advantageous over computer-based games for what is essentially a simulation:
...you can constantly tweak the rules to take account of new insights, says Timothy Wilkie of the National Defence University in Washington, DC. With computer games, this is much harder. Board games can also illuminate the most complex conflicts.
Warfare is rarely willingly indulged by all parties.
Try "never" willingly indulged in by all parties. The civilian population in wherever the war is taking place has absolutely no say in the matter. And if some kind of draft is involved, then neither do many of the combatants.
Also, there is the simple fact that some wars can't be won, even if you fight them: If the US nukes more of Russia than Russia nukes the US or vice versa, then almost everybody is still dead, because the long-term effects of the nukes in the atmosphere will do in both sides and everyone else caught in the middle (except for those few who survive in the bottom of some of our deeper mine shafts, so long as we don't have a Mine Shaft Gap!)
I prefer to reserve absolutes for mathematically provable claims. There is no reason as to why it's impossible to have a war where all parties participate by choice, it's just extremely improbable given human nature.
To disprove an absolute, you'd need a counterexample. There simply isn't one in recorded human history. That's as close as you'll get to an absolute in any non-mathematical field of study.