[Cthulhu_]

Flattening a city doesn't win a war. They started the war with the intent of driving tanks into the city and overthrow the government in three days, but (as the article mentions) that didn't work out.

But flattening cities is a WW2 strategy, and it didn't actually do much to win the war in the end, only cause unnecessary civilian suffering.

[ExoticPearTree]

If you flatten all of them and kill the residents, you will win the war. The question is just how far are you willing to go, not the lack of capacity to do so.