This is what democracy is, a coarse estimate of who has the most soldiers. A 90% majority can do what they want, a 51% majority needs to compromise a little.
However, in an actual war many things matter more than the numbers or fighting power. For example, it is clear that ISIS is much weaker than the full USA military, however, because defeating ISIS in an actual land war would cause significant casualties to USA, they can go on - a clear simulation result showing that they would lose won't ever be enough for them to concede defeat since they can (and will) simply call it as a bluff and claim that USA is not willing to pay the blood price. So you can't settle a conflict like this with a simulation; the loser always has the backup plan of telling "make me, if you dare" instead of accepting the loss.
Agreeing to a result of simulations that both sides believe isn't settling undecided disputes nonviolently, it's just old fashioned diplomacy or ultimatum/surrender.