How does a stateless society (anarchy, comunism...

how does a stateless society (anarchy, comunism, whatever) protects it's citizens from another state that wants to conquer it?

Apparently, things like that don't happen in fantasyland...

Citizen militias and private mercenaries,

the invaders will be stopped by the lack of roads

What if the opposition simply offers to pay more money to the mercenaries?

how does a citizen militia can realistically beat an entire enemy state army with trained soldiers and military gear?

Won't happen if you just make the whole world stateless :^)

See world war 2 Russia. Draft the population.

Such a society cannot protect its citizens, that's why such societies don't exist. commiefags like to claim that "real communism" has never been done, and they're right because it's completely fucking impossible

It doesn't. Kek