In a conventional setting, the US army is peerless. However, in an insurgency setting, the limitations have been exposed.

If the military chose to, they could level Iraq and Afghanistan in a week. But since it is abiding by COIN rules of engagement, it obviously cannot unleash maximum force on the enemy.

The US army was hurting after the Vietnam war and many speculated they would lose at the hands of Warsaw Pact forces if they ever decided to push west – but after a lot of innovation, retooling, and implementation of improved doctrines (the AirLand Battle Doctrine for example), they brought it back to the being the best military in the world.