Can you explain why this is true? It's a very strong claim.
for small groups nearly every dispute could pose existential risk, but for enormous groups very few disputes pose existential risk. then in the conflict side, enormous groups have MAD, where conflict itself carries existential risk. small groups of course can also be wiped out by conflict (even if they don't possess a bureaucratic mechanism to ensure that,) but the risk side of the calculation is heavier for them I think.
and enormous groups still engage in conflict with each other although it happens indirectly via proxy wars.
also paradoxically the larger the group becomes the more its interests, or "meta interests" (such as favoring stability and security), tend to align with its competitors but for small groups it's almost like every group for itself. but I believe that the calculation can tend towards cooperation being more beneficial the larger group gets. but I think this factor only applies when groups become very very large.
also there's some sort of entropy argument as in large groups cultivate more structure, organization and order and therefore it would take more energy to dismantle them so they're more stable. which not only makes them harder to dismantle but also gives them more to lose if they were to decide to tear everything down and build it up again.
that's how I think about it. what do you think?
If I put myself into that situation for a moment, as the leader of a small armed group, I can see two options at first. The first option is to go into hiding and potentially die of resource starvation if I am unable to cultivate the things needed to survive on my own (or be killed by outside attackers). The second is to grow bigger and bigger by forcibly and preemptively taking over the other small groups so I can secure my borders so to speak, but going on the offensive can also lead to premature death as well.
As a result I think some hybrid approach is needed, where one goes into hiding in a land so far away and inhospitable that nobody wants to attack, thus there's nobody to fight.
Incidentally, 19th-century America had a lot of faults and flaws (it was incredibly racist), but an absolutely unprecedented amount of scientific and industrial progress was made without much public spending at all.