( CNN) The scent of chaos hangs heavy in the air. Donald Trump evokes it in Cleveland. Islamic State sows it in Nice, Brussels, Paris, Orlando. Britain is immersed in it after Brexit, while the EU struggles to prevent its onset amid mounting crisis of migration and political legitimacy. Ukraine and Syria are being torn apart by it, and Turkey looks fragile after a failed coup.

To apply a metaphor from the social sciences of chaos, we are, it seems, in a moment of phase transition. A nation of relative global order — the Long Peace, as Steven Pinker describes it in “The Better Angels Of Our Nature” — has existed since 1945. We’re now moving into a new configuration of vying powers and ideologies, the structure of which we cannot predict, except to presume it will be very different from what we have known.

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