We'd give them our low paying jobs, oh wait.... thats already happening.
allowing for some mighty powerful handwavium that lets an enemy get a an army big enough for a sustained invasion to our shore. There are still more guns than Americans and almost as many sources of explosive or flammable materials. Also because or urban sprawl most major transportation hubs are surrounded by civilian dwellings providing a ready see of fishes for the American insurgents to reside.
Granted an insurgency alone cannot win a war vs a ruthless conventional army. But when those insurgents work with and support regular army, national guard forces and police forces.