We all know the what war was like in the Middle Ages, right? A bunch of rich guys get on horses and run into each other with lances, swords, and axes until one of them can't any more. And... that's pretty much spot on. But! How did the world (or at least the West, but come on, that's the important part of the world, right?) come to that state of affairs? How did we get from the Roman army -one of the most well-trained, well-equipped, and efficient killing machines ever- to an "army" consisting of a few hundred individuals trying to run over each other with horses? The answer to that question is the subject of C.W.C. Oman's classic The Art of War in the Middle Ages.
And it is deservedly a classic. Despite only being 165 pages long, Oman packs in both a relatively fast-paced narrative (he does cover almost 1200 years, after all) and lots of interesting details. Also impressive: he wrote what has become the definitive text while an undergrad at Oxford in 1885. [Sigh] I've wasted my life...
As mentioned, the book covers a 1200-year stretch, ranging from destruction of the last "real" Roman army by heavy cavalry at the Battle of Adrianople (378 A.D.) to the last major victory of heavy cavalry at the battle of Marignano (1515 A.D.). The stretch of time between these two battles saw the rise, dominance, decline, and collapse of armored horsemen on the battlefield. Through these centuries developed not only a style of warfare, but an entire way of life entirely focused around the idea that cavalry was supreme in the art of war.
How did this happen? It began with the size of the Roman Empire and the series of Civil Wars that plagued the Empire at the end of the Third and beginning of the Fourth centuries A.D. For nearly 600 years, the Roman legion (infantry) had been the dominant military force in the world. A series of civil wars (which Oman does not discuss) depleted the Roman legions, forcing each successive Emperor (and their challengers) to rely increasingly on barbarian mercenaries (usually cavalry) to fill out the shrinking ranks. This meant that money and training were flowing at a steady pace from Rome to tribes outside its own borders. When the Civil Wars came to a (temporary) end with the accession of Constantine (303 A.D.), there was so little left of the old legions that Constantine simply reshaped the army around cavalry. This had the dual benefit of utilizing forces already employed by the Empire (though not native Romans) and giving the new army sufficient speed that it could reply to barbarian incursions anywhere in Europe much faster than the old infantry-based legions. On the other hand, it meant that 1) Roman citizens no longer filled the ranks of the military, and the loyalty of the army was now only the loyalty of paid mercenaries; 2) even as the barbarian cavalry became increasingly important and the remaining Roman legions increasingly ignored, ill-trained, and ill-equipped, tactics did not change. So when the Emperor Valens led the remnants of the Roman army (~25,000 men) against the Gothic cavalry, he did it as if he were leading the same trim and well-fed legions that Caesar had led against the virtually naked barbarian horsemen of four hundred years earlier. The result was the utter destruction of the Roman Army, the opening of the way for the barbarians into the heart of the Western Empire, and the establishment of cavalry as the force to be reckoned with on the battlefield for over a millennium.
Oman gives three quick surveys of the development of warfare. In the first, he talks about the rise of the military class (knights, chivalry, and all that) and the final destruction of the infantry holdouts in the West (mostly in England and Viking nations, all of whom eventually "converted" to cavalry). Two of the common assumptions of this time are that 1) war is a matter of hard work and courage, not of any kind of tactics or skill. That is, a single knight with enough boldness can only be stopped by another knight with equal or greater boldness. No foot soldier will ever stand against a charging armored horseman; 2) those who meet the conditions of 1) are better (both morally and socially) than those who do not, especially than those who do not even try. So we see in warfare a microcosm of the principles of feudalism (or perhaps vice-versa).
In the second survey he discusses the development of war in the Byzantine Empire (on which he has a whole book). Only in this remnant of the Eastern Roman Empire does war survive as an "art", where it is studied, practiced, and engaged in by professional generals and professional armies. Yet, even here the transition to cavalry is made, though in a more limited and mixed way (the Byzantines keep the old Roman artillery, for example, and even expand on it with the invention of Greek fire...).
In the third survey, Oman explores the centuries of the dominance of heavy cavalry (roughly 1066-1346). In this time in the West, tactics, organization, and cohesion of large armies are virtually unknown. "Battle" consists of two armies of heavily armored nobles (and their feudal hangers-on) smashing into each other until one side quits and goes home. Endurance and courage become the virtues necessary to win battles. Which means that 1) any use of even the most rudimentary tactics usually defeats these Medieval "armies"; 2) if there is any chance that sheer hard fighting will win the day, these Medieval "armies" will usually overcome. The Crusades -aberrations in Medieval warfare though they are- are remarkable examples of both of these points. Whenever the Muslims had qualified leadership, they won. Whenever it came down to who could fight harder or longer, the Crusaders won.
In the last chapters, Oman discusses how the dominance of cavalry in the Middle Ages came to an end. Namely, through the return of infantry. In Switzerland and England two styles of combat arose which utterly defeated the usefulness of the heavily armoured horse on the battlefield (Bohemia and the Ottoman armies are briefly discussed as well). The use of the pike and halberd in Switzerland and the use of the longbow in England (and the war wagon in Bohemia and gunpowder in the Ottoman army) unhorsed the cavalrymen so severely that he has never made a comeback. Oman then discusses how these innovations were themselves made obsolete by the rise of combined arms and new technologies at the beginning of the Early Modern Era.
Really, this book was just a delight to read. While it may not be for those who aren't interested in military history or the Medieval world, I found it fascinating and worth a second look (the first being in undergrad, where I may have just skimmed it...). In fact, it's good enough that I'm going to keep my eyes open for his longer and more mature two volume edition.
In addition to recommending this to Medievalists and military historians, I'd recommend this to anyone who wants to write history. Oman's style is short, full, and readable. He conveys a lot of information in a few words without being boring. If more history books were written like this, we'd have more people interested in history.