“But Schlieffen died in 1913, a year before the war, and the German general staff didn’t quite execute the plan according to his design. Always fearing the unknown millions of troops the czar might throw at them, they took two divisions from the west to bolster the east. Then they spared the right, up here by Belgium, to strengthen the middle. And perhaps the biggest mistake is that this army turned in too soon, exposing its flank to Paris.”

After drawing the arrow for von Kluck’s blunder, Donahue shook his head. “Remember—all of this is based on train schedules and planned with minute-by-minute detail, down to the number of axles that would pass over a given bridge within a given time.”

Donahue scratched his nicotine-stained mustache. He had round, rimless glasses and looked like a distempered, gray-badger version of Teddy Roosevelt, running on coffee and low-tar Camels. Dan could smell his skunked breath from the third row.

“Von Moltke, the chief of the German attack, expected to conclude the west by the thirty-ninth day of the war, and then the real threat—the Russian front—required this huge transfer of troops and materiel starting on day forty.

“This was what the Germans feared, having to fight a war on two fronts. Schlieffen on his deathbed told them, keep this right wing strong. But they hedged, and then the armies didn’t quite meet up properly to encircle Paris. Which sets up the Battle of the Marne and a crazy last-ditch effort where the French commandeer every last taxi in Paris to race six thousand troops to the line. This miraculously thwarts the German advance and throws Schlieffen’s timetable out the window.

“So, gentlemen, as von Moltke feared: ‘No plan survives first contact with the enemy.’” Donahue turned to his sophomore class and placed a brown boot up on his desk. He had been a marine in Vietnam, which no one dared ask him about, and was still an active drill sergeant in the National Guard: talking and shouting were equal registers of discourse. “How this war started, how this all came to pass, is the result of a long chain of dominoes that we’ve been looking at in the century following Napoléon. The delicate balance of power established at the Congress of Vienna is thrown off by the assassination of Ferdinand and the goddamn Serbians’ acceding to all but one demand in the ultimatum! Old alliances become entanglements. The British don’t send enough support to the French, who, trying for a quick strike, ran right into the German war machine. The Russians are ridiculously slow to mobilize, but their backward country is impossible to invade because their trains run on an antiquated gauge.”

Stepping to the right of the whiteboard, Donahue retracted the great-powers map, which was mounted on spring rollers. All of Europe snapped up to the ceiling.