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 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. These technologies are all for defense, not power-projection.
This has a similar effect as the development of the musket in the 1500s. 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. This reversed with rifles (their greater accuracy benefitted from more professional training) and modern armor & explosives (which required an industrial base and supply chain greater than any city could muster), ushering in the era of nation-states. Military technology is changing again, and that's why I believe the nation-state system is again going to revert to smaller decentralized units.