Yeah, I know the 'rule'. The least messy war that comes to mind is the first gulf war, and that had loads of direct targeting of civilians[0]. Most wars (second gulf, various israeli wars, etc) are way worse. I cannot in fact think of a single example of the rule being followed, can you?

If you consider a really bloody war, like the korean war, they killed a fifth of the population of north korea, and destroyed basically every single piece of civilian infrastructure.

[0] https://en.wikipedia.org/wiki/Gulf_War_air_campaign