Boettke sets up the situation

There was a presumption toward voluntarism in human affairs, but in recognition that our nature is divided between a cooperative nature and an opportunistic nature we must figure out a way to curb our opportunistic side if we hope to realize the fruits of our cooperative side. While our cooperative nature is reflected in our propensity to truck, barter and exchange (which no other species actually exhibits), our opportunistic side is revealed in the warring nature witnessed throughout human history. Political economy solved the puzzle by suggesting that we could sacrifice in a small way the presumption of voluntarism in order to create a government which will curb our opportunistic side and enable our cooperative side to flourish. Thus was born the argument for limited, but effective, government that was the core of classical liberal thought from John Locke, David Hume and Adam Smith to more contemporary writers such as Frank Knight, Ludwig von Mises, F.A. Hayek, Milton Friedman and James Buchanan.