Aussie_Lurker
Deity
I've never seen any warfare that was "humane."
(rummages around in my quote pocket...)
"The essence of war is violence. Moderation in war is imbecility." -British Sea Lord John Fisher
But seriously, razing cities already does carry a diplomatic penalty.
Well, just spitballing, but how about this:
The <City Name> Convention Resolution:
Effects: 1. Civilian Units cannot be killed/captured, only displaced to the nearest city.
2. Diplomatic Penalty for attacking cities, double diplomatic penalty for *razing* cities.
or 2. Units gain a penalty for attacking cities, double diplomatic penalty for *razing* cities.
Aussie.