I find it funny that unofficial armies (guerrillas?) are able to go toe to toe with state militaries, holding their own incredibly well, while said state militaries struggle so much. Why is that?
New technology is shifting the balance of power. Stuff like drones didn't exist until fairly recently, and western military doctrine doesn't account for them. Drones are very cheap to produce, costing mere thousands of dollars, and they're difficult to intercept. This piece of technology pretty much invalidates the whole US air defence strategy. It's simply not cost effective to use million dollar missiles to intercept cheap drones.
I imagine the bigger problem is going to be lack of industrial capacity. Most of the supplies come from existing stocks, but once those run dry there's gonna be a problem because US can't produce missiles at the rate drones are produced.