There are no just wars and no good guys and bad guys in war. Just poor suckers killing each other because some politician decided they should.
The rational thing for the politicians to do is initially be pacifist and try at all costs to avoid a war and then if that finally fails become ruthless and meticulous and deadly.
The British did it right in WWII. Chamberlain was essential attempt at pacifism (which maybe went on a touch to long) and Churchill represented the flip side of ruthless pragmatic killing at all costs once the pacifism had failed.
In recent history George W Bush got it wrong on two counts.
First he was jumping willy nilly if not gleefully into wars for political personal and ideological reasons and far far to early with little reason or cause. No attempt to explore other options, he was too gun happy and gave the impression he was off on a deer hunt.
But even worse once he committed he was half-hearted about it, pretty much assuming the other side would somehow be awed by his impressive military strutting about and just roll over and play dead while the populace would welcome him and the troops would be home by Xmas
It's like the old street fighter adage "Do not threaten with a knife. You never pull a knife until you have no choice because once knives appear someone is going to get messed up".