In Guns Germs and Steel Diamond also makes the point that life as a peasant farmer kind of sucks versus that as a hunter gatherer. It's 12 hours a day of back breaking grind for a limited range of foodstuffs that often don't cover nutritional needs. So communities only adopt it under competitive pressure, because a community of farmers can be much larger and hence dangerous in war against a community of hunter gatherers on the same land.
I think the English experience in Sydney and Parramatta with the Eora and Dharug in the 1780s showed that it doesn't have to be war, just competition for land. The establishment of agriculture makes the land unusable for hunter-gatherers.
'Sworn to no party, and of no sect am I.' Frederick Vosper's republican motto.
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