Any invading force that can get by the US military is not going to be worried by its armed citizenry, not matter how many times you watch Red Dawn
You overestimate the US military power and hugely underestimate the power of an armed citizenry.
During the revolutionary war the colonials were mere farmers with the worst weapons you could have going up against the worlds most powerful empire at the time.
Look at what the Mujahideen had done to the Soviet Union when they tried to invade! The Soviet Union was arguably the most powerful military in the world at the time, and they couldn't get past a bunch of unequipped guerrilla fighters in the Hindu Kush.
Just look at the comment above you talking about the Japanese Admiral. It's not made up.