Monopoly is the byproduct of allowing centralized power, not the natural state. I'm not actually sure how we could narrow down the natural state of humans at this point, but I strongly suspect it wouldn't be based on an assumption that people are willing to give up a growing list of individual freedoms in the name of fear.
Stopping the accumulation of power requires aggressive sacrifice from the less powerful.
This isn’t a feature of humans, but basic system dynamics / economics / etc.
A group gets more power and leverage that power to gain more power. Inevitable. Coordinated action is the only way to prevent it. And coordinated action is government.
Stopping accumulation of power is very hard when you have no accumulated power. I’m not sure how you could possibly believe otherwise unless you’re one of those believers in magical harmonious anarchy
So when you have $10 and your neighbor has $200 in whatever assets or currency your little community needs, and your neighbor decides to invest it, you’re gonna what, attack him? Gather your other neighbors and demand he share?