A large part of being effective at scale is not just having lots of workers, it's about having the right workers doing the right things at the right place and time.

One of the reasons the American military is so impressive is its ability to mobilize and coordinate quickly. This isn't an accident. Military training isn't just "this is a gun, point it this way," but there are layers and layers of specialized skills there. I don't care how many hundreds of yahoos you have in a small town with rifles. They would get rolled over by a small company of professional military with proper training and equipment.

That's not saying that if we were invaded that there might not be an armed insurgency, but at that point, it's less about an organized force and more about an informal resistance.