An alternate future where war is waged by machines, by drones under the control of a sentient controller that monitors the borders and airspace of its host nation. Its neighbor states are similarly automated and any conflict becomes a stalemate, as no nation has an advantage. The controllers communicate amongst themselves to avoid surprises and needless loss of equipment. Even the ground crews are automated/robotic.
No contact between these nations is permitted. The drone forces control all travel and communication.
The conflict: There is resistance to this control. Some people want to visit other nations in the region but cannot. What happens when one side in a contested/patrolled area finds a human on the opposing side? The core principles of the controllers and each drone prohibit harming humans. But this human is using that rule and the fact that it can operate outside the understanding of the systems to upset the balance. It can only be detected visually.
Humans do not show up on sensors, the sounds they make are too irregular to detect, and they have jamming tools that broadcast false information. How do the other nations respond? Field their own human fighters? Remove the ban on harming humans? Can they agree to allow travel? Or are the reasons for banning it forgotten?