Earlier quoted context omitted.
Defense economics will prevent this transition to city-states from happening.
I would've agreed with you until about 5 years ago. The reason I disagree with you now is because technology and methods of war-fighting have changed. Emerging defense technologies like drones, lasers, robots, micro-scale manufacturing, and self-driving vehicles - along with the latest generation of existing weaponry like MANPADS and anti-tank missiles - all preference the defender. They allow a group of relatively u…
> They allow a group of relatively untrained and loosely organized defenders who know the terrain well to deploy extremely effective resistance against an attacker, as long as it's at short range. A drone swarm can quite literally destroy all hostile forces within an area without risking a single person, but it can't do this beyond say 100 miles out.
We already have this "drone swarm", we just call it a guided missile.
The hard part in fighting a modern army isn't killing them, it's finding them. The defender is inherently at a disadvantage in this regard because they have things to defend, which necessitate that they're position in the vicinity. Russia is struggling at the moment not because defenders are inherently advantaged but because they're relying on conscripts and relatively untrained soldiers.
> The musket allowed relatively untrained militias to enjoy superior firepower over the knights and longbowmen that had trained professionally their whole lives. As a result, smaller city-states and colonies could defend themselves against the large standing armies that kings and emperors could wield, and so the feudal system collapsed.
The exact opposite of what you're describing happened with the wide utilization of gunpowder. Pre-gunpowder, city-states and small kingdoms enjoyed relative independence due to the sheer expense of penetrating walls. Post-gunpowder, artillery (not rifles) required a whole professional organization to be utilized effectively, and formed the backbone of the army, so small states could no longer field or effectively defend against larger states, leading to increased centralization of authority, well before the creation of nation-states. "Makers of Modern Strategy from Machiavelli to the Nuclear Age" covers this transition pretty extensively.