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The heavily analyzed Schlieffen Plan was the perfect invasion strategy, and the hardworking officers of the German General Staff knew it. The basic idea traced all the way back to Hannibal. That’s not the Hannibal known to Americans today as the vicious yet urbane criminal mastermind of book and movie fame, but the original: Hannibal Barca of Carthage, one of the greatest battlefield commanders in history. If you needed a good way to win—and win big—it only made sense to look to Hannibal.

In his most decisive victory, Hannibal cornered a Roman army sent to stop him. The two forces met on August 2, 216 B.C., facing off across a hot, flat plain called Cannae, south of Rome. Tempting the overly aggressive Roman commander to attack, Hannibal pulled back his center troops. Sensing Carthaginian weakness, exultant Roman foot soldiers surged forward. As they did, Hannibal swiftly swung in both of his flanking contingents, bagging the stunned Roman legionaries in a double envelopment. More than 60,000 trapped Romans died in the resultant slaughter. Historians rightly acclaimed Cannae as a brilliant battle of encirclement and annihilation, with due credit to the vision and leadership of the intrepid Hannibal.

Of course, one win does not a final victory make. People still know about Hannibal, but as for Carthage, not so much. The Romans learned from the Cannae debacle. Chastened, the legions reorganized, retrained, reequipped and struck back, grinding toward Carthage in campaign after campaign. Eventually, after killing thousands of their opponent’s best troops, Rome’s hard-bitten legionaries took the fortified city of Carthage itself. They smashed the stout walls to dust, pulverized the neighborhoods block by block, put most of the men to the sword and sold the surviving population into slavery.

More than 2,000 years later, at the dawn of the 20th century, the German General Staff—especially its dour chief, Field Marshal Alfred von Schlieffen—saw only the glittering promise of a smashing, Hannibal-caliber envelopment. Schlieffen venerated Cannae. His staff diagrammed it, dissected it and sought to replicate it. Having smashed the Danes in 1864, the Austrians in 1866 and the French in 1870–71, Schlieffen’s officers figured that if anyone could pull off a modern Cannae, it must be the guys in gray with the spiked helmets.

The Germans needed a Cannae. Geography dealt them a bad hand. The General Staff in Berlin faced known enemies on two fronts. To the west, the vengeful French marshaled their regiments, waiting for a chance to redress the humiliating failures of 1870–71 and retake their lost provinces of Alsace and Lorraine. To the east, the disheveled but energetic millions of the Russian Empire threatened to roll across the frontier. So the top graduates of the Berlin War Academy, the famous experts of the German General Staff, wrestled with the same dilemma that plagued their country again and again: How do you win a two-front war?

Before Schlieffen’s time, Chancellor Otto von Bismarck and his General Staff chief, the elder Field Marshal Helmuth von Moltke, didn’t resort to Hannibal or hope. To deal with the two-front problem, they just said “no.” Both men accepted French enmity, but the war of 1870–71 indicated that France alone could not beat Germany. The key was to keep France isolated, so Bismarck wove elaborate diplomatic schemes to ensure good relations with Russia. For his part, von Moltke drew up defensive plans to avoid provoking Germany’s powerful eastern neighbor. It made all the sense in the world. After 1888, however, the new German Kaiser, the headstrong Wilhelm II, did not agree. He dumped Bismarck, retired von Moltke and watched calmly as Russia and France entered into formal alliance. Wilhelm II didn’t fear a two-front war. Confident in Germany’s burgeoning strength, he intended to win it.

Thus, Schlieffen and his General Staff mavens were told to design a perfect plan to win a two-front war. They started with a big assumption on timing. In the west, the French would mobilize in two weeks and attack into Alsace-Lorraine. To the east, the Russians would take six weeks to gather their forces before attacking. German intelligence was reliable, and both adversaries were not all that careful about concealing their plans. General Staff officers in Berlin crunched through population demographics, industrial production figures, map measurements and railroad statistics, but the numbers consistently told the tale. Beat the French in six weeks, and then race the German divisions across the country by rail to deal with the slowerarriving Russians. The trick was ensuring an early knockout punch in France. As was their wont, the General Staff looked for relevant historical examples. Schlieffen and his men came upon Hannibal at Cannae. That would do.

By 1905, the perfect plan came together. To ensure rapid, decisive victory in the west, Schlieffen devised a modern Cannae on a continental scale. The General Staff amassed a crushing superiority against France, outnumbering the French almost two to one. Two of the German corps defended Alsace-Lorraine, beckoning the French to plunge forward to reclaim their lost provinces, as Schlieffen well knew they wanted to do. While the French attacked, the bulk of Schlieffen’s forces would sweep out in a great arc, marching through neutral Belgium, “letting the last man on the right brush the [English] Channel with his sleeve,” in the field marshal’s descriptive phrasing. This vast German array would descend on their foe’s rear echelon, cutting off French forces in Alsace-Lorraine, outflanking the panicked citizenry of Paris, and ending the war in the west in 42 days. The French were assessed as squabbling, excitable amateurs certain to advance merrily into the fatal trap. The few British divisions amounted to what the Kaiser dismissed as a “contemptible little army.” The Belgians were discounted altogether. The morality of bludgeoning through a neutral country did not figure in Schlieffen’s calculations.

Clearly, Schlieffen took a lot of risk in the east. Only two corps would hold the line as the Russians built up, but the Germans thought little of the Russians. Tsar Nicholas II appeared weak and easily confused, his armies humbled by the Japanese in a brutal 1904–05 war, his restive populace shot through with revolutionary sentiment and hobbled by widespread illiteracy. The supposed “Russian steamroller” leaked steam at every joint, and the roller looked pretty cracked and rusted. The tsar’s hapless hordes would be easy prey once France had fallen.

The Germans rehearsed their perfect plan over and over. Mobilization drills linked up 2 million men, weapons, uniforms, supplies and horses at key German railway stations. Then, in an intricate, well-oiled ballet, more than 200,000 rail cars practiced forming into trains and heading west. When German mobilization ran flat out, one troop train crossed the Rhine River at Cologne every six minutes, monitored by General Staff men with perfectly synchronized stopwatches. Schlieffen’s successor, the younger Helmuth von Moltke, tinkered with the details. He moved two more corps to the east—you never knew with the Russians, since they might be early—and shifted six more corps into Alsace-Lorraine, just in case the French got lucky. But that still left 27 German corps to make the big envelopment. The basics remained intact: blow away France with a massive right wheel through neutral Belgium, then use the wonderful German railway network to speed the victorious veterans to the east to clobber the slow-assembling Russians. It was massive. It was beautifully crafted. It was perfect.

On August 1, 1914, von Moltke got his chance. A fracas in the Balkans pitted Austria-Hungary against Russia. Ever excitable—and a bit fuzzy on the current war plan—Wilhelm wanted to support his Austrian ally without tangling with France or bringing in Britain by violating neutral Belgium. Hearing the Kaiser’s intent, von Moltke nearly passed out. With all the tables of figures, all the battle drills, all the practice maneuvers, the millions moving, the hundreds of trains clicking west, von Moltke gasped, “Your Majesty, it cannot be done.” The great German General Staff, the finest military minds in Europe, the scions of the great Hannibal, had only one plan. They had to attack France. They had to go through Belgium. And so they did. T he perfect plan came unglued almost from the start. The German General Staff could control the railroads and the supply depots, but couldn’t direct the activities of their enemies. The Belgians resisted and did so fiercely, gumming up the timetable. Four tough British divisions, manned by sharpshooting regulars with bolt-action Lee-Enfield rifles, convinced battered German divisions that each opposing battalion fielded dozens of machine guns. The French pushed into Alsace-Lorraine right on schedule— and failed in a bloody riposte—but they also rapidly assembled tens of thousands of spirited reserves and disciplined colonial troops to block the great German right wing. At the six-week mark, just as Schlieffen predicted, the climactic battle of France occurred on the Marne River, but the wrong side won. Exhausted German troops faltered and fell back.

The perfect plan didn’t allow for that. There was no Plan B. Four horrific years of trench warfare ensued. A century later, what can we learn from Schlieffen’s perfect plan? Rather than trying to conjure the ghost of Hannibal, Schlieffen and his proud General Staff cadres might have been better served to look to one of their own, Carl von Clausewitz. In his magisterial work On War, Clausewitz, who had fought in all too many battles, warned of what he termed friction: “Countless minor incidents—the kind you can never really foresee—combine to lower the general level of performance.” Clashing armies, bent on mortal combat, generate friction as surely as two sticks rubbed together. It’s as endemic to war as wetness is to water. No computer, no secret weapon and no trickery can banish friction. That was true in France in 1914. It’s true today. Beware the perfect plan: It will fail. And then what? In 1914, the result was World War I. A hundred years later, it’s a sobering reminder of the high price of military arrogance. We do well to keep it in mind as we fight today’s wars and prepare for those to come