Why did humans adopt agriculture in Neolithic times? Our intuition would say because it has better nutritional outcomes. But the evidence points to the contrary: the bones of early farmers consistently show poorer health than the preceding hunter-gatherers. So why would agriculture be adopted if it lead to a disadvantage?
Robert Rowthorn and Paul Seabright say it was individually rational to adopt agriculture, even though it was detrimental to society, much like in a prisoner's dilemma. The problem of a farmer is that he needs to defend his land and his cattle. That seems an additional disadvantage with respect to hunter-gatherers. But farmers can team up in villages, and fortify them. And voilà, now that they have a secure base, they can start raiding around them instead of only defending. This is where the prisoner's dilemma comes in: it is individually rational for every farmer to dedicate resources to defense, but this lowers everyone's welfare.
And thus started the grip of the defense industry on the economy.