Military science is far from an exact science, as Grant, Rommel, Clausewitz, Tolstoy, and other chroniclers of war have long argued. The tide of battle often depends on human factors--bad information, miscalculations, happy guesses, thorough planning--and on quirks of weather, timing, or faulty equipment. By providing all relevant information that Napoleon, Lee, Washington, and Henry V had at the ready, Yours to Reason Why isolates the moments when...