John Keegan is an accomplished military historian, and his book The Face of Battle is an unprecedented analysis of combat. Keegan evaluates three historic battles from three very different time periods: Agincourt, Waterloo, and the Somme.

Keegan makes it clear from the beginning of his book that he is not a veteran of wars, but rather a student of them. He has gained great knowledge through primary sources during his research:

I have not been in a battle; not near one, nor heard one from afar, nor seen the aftermath. I have questioned people who have been in battle . . . have walked over battlefields, here in England, in Belgium, in France and in America . . .

Keegan offers a definition of battle for his readers:

For there is a fundamental difference between the sort of sporadic, small-scale fighting which is the small change of soldiering and the sort we characterize as a battle. A battle must obey the dramatic unities of time, place and action.

In addition, Keegan provides insight into the commitment of soldiers to their duties throughout the centuries in nations around the world:

While the great armoured hosts face each other across the boundary between east and west, no soldier on either side will concede that he does not believe in the function for which he plans and trains. As long as states put weapons in their hands, they will show each other the iron face of war.

In the next quote, Keegan analyzes the relationship between soldiers and their leaders:

What sustained men in combat like Agincourt, when the penalty of defeat, or of one's own lack of skill or nimbleness was so final and unpleasant? For the English, the presence of the King would have provided what present-day soldiers call a "moral factor" of great importance. The personal bond between leader and follower lies at the root of all explanations of what does and does not happen in battle . . .

Additionally, Keegan examines specific battles. In the following quote, he analyzes Waterloo:

If the story of Waterloo has a "leitmotiv" it is that of cavalry charging square and being repulsed. It was not absolutely inevitable that horsemen who attempted to break a square should fail. . . . The feat of breaking a square was tried by French cavalry time and again at Waterloo—there were perhaps 12 main assaults during the great afternoon cavalry effort—and always (though infantry in line or column suffered) with a complete lack of success.

In his scrutiny of the long, costly Battle of the Somme, Keegan shares the thoughts of many about the conflict:

Accounts of the Somme produce in readers and audiences much the same emotions as do descriptions of the running of Auschwitz—guilty fascination, incredulity, horror, disgust, pity and anger—and not only from the pacific and tender-hearted . . . but also from professional soldiers . . . Why did the commanders not do something about it? Why did they let the attack go on? Why did they not stop one battalion following in the wake of another to join it in death?

Providing a glimpse into the real people of various armies, Keegan also offers interesting anecdotal remarks about unique soldiers in the field:

Rundstedt, revered throughout the German regular officer corps as its last archetypal Prussian, refused to deal with detail or to look at small-scale maps, as if the fighting itself were distasteful to him, but spent his days reading detective stories and thrice resigned his command

Keegan also offers a perspective on the impact of both World Wars upon humanity:

The very scale of the First and Second World Wars has determined that . . . the experience of violent and sudden death has been brought through battle into many, perhaps a majority of families, that fear of the suffering—arbitrary and accidental as well as deliberate and purposive—battle can cause to human societies is profound and almost universal, and that the usefulness of future battle is widely doubted.