~200 years into the future, most of mankind has been wiped out by war. The remainder lives in walled supercities, to protect them from the hazards of the wastelands - including a nation of machines intent on human extinction. I've been thinking of ways to give the humans a fighting chance, while also restricting long distance travel, one of them being to remove flight from the equation. This includes missiles, rockets and aircraft.
In a world where cybernetic mods, artificial intelligence and genetic engineering are day to day things, what reason would there be not to have any form of flight?
Edit: For clarity by aircraft I mean planes, helicopters and drones. Airships and gliders are slow enough to be shot down by almost anything so they don't matter.
Basically no faction should even want to consider investing in aircraft.
So I am seriously amazed by how much feedback this question got - you guys are awesome.I've chosen Tim B's answer because I feel it is the most comprehensive way to prevent all flight. Kudos to the AA platform ideas too, as well as the gen-modded attack birds.