We are rapidly moving towards the science fiction reality of a large plane flying over a city and dropping thousands of small, cheap, autonomous drones. The drones just hunt down all life. Then you just keep the city, infrastructure and all.
When you think about Russia and China and not adhering to international law, you could imagine a total war scenario where they use chemical and biological weapons to do just this. Imagine a drone force deploying over a city at night, dispersing the agents into the air and water. People would never know what hit them.
How would these drones deal with people who reside inside buildings which have physically enclosed interior spaces, such as houses, apartments, tenements, or large sheds and tents?
Unless special preparations are made, city-dwellers have to come out sometime, don't they?
I suppose the military will just wait patiently for their citizens to be starved out by quadcopters.
Generally if an enemies large slow military transport plane is flying over your city, your military is already losing.
One suicide explosive drone opens a hole, the next goes into it.