Before bombarding a city...

[battery]

If I were a military commander charged with assaulting a city under hostile control, I would give a 30-day advance warning to its occupants.

Every civilian is hereby given a choice. He can elect to retain his status as a civilian by leaving the city, or he can give up that status by staying behind. Everyone who remains in the city will naturally be considered as enemy combatants, informants, and assistants. Those in uniforms will be treated according to rules of war. Any person found without a uniform will not enjoy such protection. If captured, he will be executed just like a spy.

A real civilian in a combat zone must not interfere with war operations. His motivation is to stay out of harm's way. Any action inconsistent with this goal will put his civilian status in doubt.

Obviously this goes against the Geneva conventions. But do think about why soldiers want to capture cities. From a military standpoint, a city provides a bunch of hideouts for infantry, making them almost impervious to tanks, artillery, and airstrikes. It is absurd to put "civilians" into the equation. These so-call civilians aren't pure civilians at all! They stay in the city because they want to provide aids to their soldiers. Actual civilians would take the first opportunities to flee the city, because they don't want to be trapped in a besieged city with water, food and electricity supply cut off. My moral standard is that anyone caught assisting combatants directly is a valid miliary target. Feeding soldiers makes you part of the logistic staff. Treating wounded soldiers makes you part of the medics corps. Putting out fire on military assets makes you part of damage control. Calling 911 to report artillery and gunfire makes you part of the milltary intelligence service. All these practically makes you a soldier.