How do you turn a metaphor into an axiom? Try: "Strategist appropriation." When writing on politics and war, this means lardering your first few graphs with maxims from so-called "masters of war," preferably Sun Tzu or Clausewitz. Their unassailable wisdom gives your argument the burnish of authority.

Graham Allison, an academic with plenty of his own Harvard authority, goes a step further. He suggests that the great historian (and not so great general), Thucydides, like Clausewitz and Sun Tzu, offers not just quotable truths but also a fundamental law about how wars often happen: The Thucydides Trap.

Allison argues that when rising powers threaten the position of established powers, the inevitable competition can lead to conflict and, eventually, war. Twenty-five hundred years ago, top dog Sparta became fearful and envious of Athens' rising wealth and arrogant pride. Two towering city-states became trapped in a thirty-year war whose consequences were tragic. Thucydides tells their story.