Guns have limited range, and are easily rendered largely ineffective (e.g. armored vehicles). Robots and other advanced weapons make direct combat entirely one sided. Surveillance apparatus allows identifying combatants attempting a guerilla warfare approach. AI could allow identifying an assassin attempting to draw a weapon and killing them before they could get a shot off. Etc.

Against the current US military I dare say that overwhelming numbers would win, against a theoretical future military that is less clear. Moreover the current US military would probably revolt if used to overtly oppress the population, but a more robotized one with humans only required at high levels might not.