[int_19h]

That is indeed the sticky question, but, again, anarchists aren't opposed to organizing either, even at scale - only that such organizing should be fundamentally egalitarian, not forced.

You can argue that hierarchical organization is fundamentally more efficient, but by the same logic authoritarian governments ought to always outcompete democracies militarily, yet it's clearly not as simple as that.

One could also argue that in a world where anarchist modes of organization are the norm, an attempt by some group to organize for the purpose of conquering neighbors would be treated as a fundamental threat by basically all other groups and treated as an imminent threat that warrants legitimate community self-defense. Of course, then the question is how you get to that state of affairs from the world of nation-states.

I don't have answers to these questions, but it should also be noted that it's not a binary. Look at Rojava for an example of a society that, while not anarchist, is much closer to that, yet has shown itself quite capable of organizing specifically for the purpose of war (they were largely responsible for crushing ISIS, and are still holding against Turkey).