Sorry for reviving this thread, but I wrote this mini-essay for something else, and I thought I'd share it here:
There are two ways to judge a military commander. The first is by the standards of how well they fought, and the second is by in what manner they changed warfare.
The first category consists in commanders that were masters of the art of war in their own era, but did not change how war was fought. The first subcategory would be excellent tacticians, or those who made intelligent decisions during individual battles. An example would be Friedrich II von Preußen, who routed a much larger Habsburg army at Leuthen by hiding behind a hill in order to march his entire army to one of the enemy's flanks, thus negating his own inferiority in numbers through local superiority. Another case would be Khalid ibn al-Walid, who was gravely outnumbered at Yarmouk, but nevertheless scored an incredible victory through his own personal cunning in wearing out and scaring the enemy into submission.
The second subcategory would be excellent strategists and logicians. They did not have to crush a stronger army in one battle; their maneuvers in the broader campaign were sufficient enough to win the war. Ulysses S. Grant is an example of this. He made numerous blunders in individual battles, especially Cold Habour, but his overall strategy was brilliant; especially at Vicksburg, where he locked a Confederate army into an inescapable position through tricky movements. Fabian or guerrilla warriors such as Chairman Mao, Bertrand du Guesclin, Vo Nguyen Giap and Skanderbeg are likewise examples of this. They were well aware that they often had little chance in pitched battles, so they chose to capitalize on when their enemies were at their weakest.
The third subcategory would be in personal charisma. Even if commanders don't win battles or campaigns, their mere presence can have a huge effect on how soldiers choose to fight. Grand Duke Nicholas Nikolaevich of Russia is a good example of this. He was not an extraordinary strategist by any means, and the Russians fared poorly on the Eastern Front of World War I. But his enormous stature, handsomeness and eloquence were inspiring to his men. Erwin Rommel was reported to have a similar effect on the Afrika Korps, and his name became legendary among the Allies. Jean de Valette and George Augustus Eliott were able to endure sieges at Malta and Gibraltar with the odds heavily against their favor through force of will and refusing to surrender.
A combination of the above three subcategories include men like Arthur Wellesley, the 1st Duke of Wellington, who -- while generally not considered to be a genius -- was an exceptional tactician, strategist and charismatic commander. He organized the Peninsular Campaign and the Waterloo Campaign, and the French were overcome not by being steamrolled by an invincible commander, but by being outmatched in resources. Another case would be Julius Caesar. He was an amazing tactician, as seen by drawing a fourth line of infantry to counter Pompey's superior cavalry at the Battle of Pharsalus. He was also an extremely effective strategist and stunningly charismatic, as shown by the conquest of Gaul and its aftermath. Other cases that encompass the above three subcategories include Alexander Suvorov and John Churchill, the 1st Duke of Marlborough. They were masters of their own era of warfare.
The second category would be in in what ways the military commanders in question changed how wars were fought. The first subcategory of this would be in technological innovations. Gonzalo Fernández de Córdoba re-organized the Spanish army to create the tercio, a pike-square formation that was undefeated for 100 years. Another example would be Helmuth von Moltke, who developed the General Staff system that was so successful for the Germans in the Austro-Prussian and Franco-Prussian Wars, that it was promptly adopted by every Great Power in the world. Strategic innovations are also to be noted; at the Battle of Leuctra, it was established that a superior army could be defeated through local superiority, and Epaminondas' echelon formation broke the Spartan army before him. Likewise, Hannibal's perfect encirclement at Cannae became the model annihilation battle that many commanders thereafter sought in their own campaigns.
The other subcategory would be in intellectual advancements. For instance, Carl von Clausewitz's Vom Kriege put an entire new frame in how war is viewed. It was so influential in the course of military theory -- especially in the notion of the "fog of war" -- that often, even today, plans are ridiculed as being "not Clausewitzian enough." Heinz Guderian's concept of the Blitzkrieg also brought Europe out of the World War I mindset. While the ultimate intent in strategies is often to cause or escape encirclement, Guderian went about it in a different way. Instead of simply outmaneuvering the enemy or denying them supplies, he would also strike at the enemy's nerve, which was principally demonstrated in the Battle of France. After breaking through at Sedan and racing to encircle all of the northern French, his lines were terribly vulnerable and prone to disaster, but the French high command was utterly paralyzed and were unable to counter-attack. Such a method of warfare would later be adopted by the Israelis in the Six-Day War.
So now, I present the case that Napoléon Bonaparte was the greatest military commander to ever live: because he encompassed everything above in their entirety. No man would deny his tactical genius at Rivoli, Marengo, Austerlitz, Friedland, Bautzen or Dresden; no many would deny his strategic genius in the Italian campaign in using his inferior numbers to defeat his enemies individually; no man would deny how almost mythological he became amongst his men and legendarily feared amongst his enemies; no man would deny that the use of the turning movement in the Ulm Campaign inaugurated an entirely new epoch of warfare; no man would deny that even today, people look back on his campaigns for inspiration for decisive victories. Although I do have to count the fact that he became sloppy and overconfident in his later years, he was simply the greatest commander to ever live. He changed the way war was processed. In the 18th century, wars were fought for typically a decade over ten square kilometers in Belgium. In a matter of a few months (August 1805 to December 1805), however, Napoléon had wiped out three Allied armies and occupied Vienna with less than 20,000 casualties. He was a born to an entirely unnoticeable Corsican family and came to be an emperor over most of Europe almost entirely through success in war. When asked who the greatest military commander in history was, the Duke of Wellington responded, "In this age, in past ages, in any age, Napoléon." As much as I despise the values that Napoléon represented and fought for, I find it impossible to disagree.
