Clausewitz would have seen coups d’oeil—“inward eyes” grasping truths ordinarily requiring long reflection.

Overstretch—the enfeeblement that comes with confusing ends and means—allows enemies to apply leverage: small maneuvers that have big consequences. Themistocles wouldn’t have won at Salamis without spinning a Delphic oracle. Elizabeth trusted her admirals to trust the winds. And Kutuzov could safely slumber after Borodino, certain that geography,

But Xerxes failed, as is the habit of hedgehogs, to establish a proper relationship between his ends and his means. Because ends exist only in the imagination, they can be infinite: a throne on the moon, perhaps, with a great view. Means, though, are stubbornly finite: they’re boots on the ground, ships in the sea, and the bodies required to fill

What, then, to do? It helped that Machiavelli and Berlin had lightness of being, for their answer is the same: don’t sweat it. Learn to live with the contradictions.

Geoffrey Parker, his best biographer, finds an answer in late twentieth-century “prospect” theory: leaders, it suggests, risk more to avoid losses than to achieve gains.76 Given the empire Philip inherited and then expanded, he had a lot to lose. What’s strange, though, are the risks he ran to regain territories he hadn’t lost. It wasn’t Philip’s

Feria was among the first, but by no means the last, of Elizabeth’s perplexed interlocutors. She could be childlike or canny, forthright or devious, brave or risk-averse, forgiving or vindictive, serene or volcanic, even feminine or masculine: “I have the body but of a weak, feeble woman,” she told her troops as the Spanish Armada sailed for home

What won the war, for the Americans, was a Machiavellian insight: that a constitutional monarchy’s humiliation of an absolute monarchy could cause the latter, years later, to rescue a republican revolutionary upstart. Still bitter over France’s loss of North America to the British in 1763, Louis XVI welcomed rebel emissaries to Paris in 1776. The

Clausewitz, in one sense, says nothing new here. Asymmetries in aspirations and capabilities have always constrained strategies, which is one of the reasons they’re needed in the first place. He’s highly original, though, in specifying friction as the cause, while showing that it can occur at any level: the passage of time and extension across

That’s because checklists adapt better to change than commandments. Sailors rely on them before going to sea. Soldiers employ them in planning missions. Surgeons demand them, to make sure they’ll have the instruments they need and that they’ll leave none behind. Pilots run through them, to ensure taking off safely and landing smoothly—preferably at