Sir John Keegan OBE (born 1934) is a British military historian, lecturer and journalist. He has published many works on the nature of combat between the 14th and 21st centuries concerning land, air, maritime and intelligence warfare as well as the psychology of battle.

Keegan was born in Clapham, the son of an Irish Catholic family. His father served in the First World War.

At the age of 13 Keegan contracted orthopedic tuberculosis, which has subsequently affected his gait. This illness interrupted his education during his teenage years; however, his education included two years at Wimbledon College leading to entry to Balliol College, Oxford in 1953. Following graduation he worked at the American Embassy in London for three years.

In 1961 he was appointed to a lectureship in Military History at the Royal Military Academy Sandhurst, the training establishment for officers of the British Army. Holding the post for 36 years, he became senior lecturer in military history during his tenure. During this period he also held a visiting professorship at Princeton University and was Delmas Distinguished Professor of History at Vassar College, a visiting professorship.

Leaving the academy in 1997 Keegan joined the Daily Telegraph as a Defence Correspondent and remains with the publication as Defence Editor, also writing for the American conservative website, National Review Online.

In 1998 he wrote and presented the BBC's Reith Lectures, entitled War in our World.

Keegan was made an Officer of the Order of the British Empire (OBE) in the Gulf War honours list and later, in the Millennium Dome honours list, he was knighted.

The long-term effects of his tuberculosis rendered him unfit for military service and the timing of his birth made him too young for World War II, as mentioned in his works as an ironic observation on his profession and interest.

Keegan is the best-known military historian of the 20th century. He is one of the few military historians not to have been a soldier, although this is hard to discern from his books, which are as concerned with the experience of the common soldier as with the tactics and strategy of the generals. This is particularly evident in The (Illustrated) Face of Battle, which discusses in detail the effect of infantry and cavalry on each other, the effects of wounds and illness, and the morale of the troops, in three successive battles—Agincourt, Waterloo, and the Somme—which occurred in different centuries but in the same region. Like all military-history texts, this book has diagrams with boxes and arrows showing movements of infantry, cavalry, and artillery units; but he discusses the soldiers in depth. He has spent most of his life training soldiers—and listening to them.

Keegan's books include a traditional battle-by-battle coverage of conflict, experience of the individual, historical causes of military events, technological change in warfare, military strategy and challenges of leaderships. He writes mainly for the educated non-specialist reader. Those who wish to sample his straightforward histories of war should read his histories of the Second World War and of, more recently, the First World War.

His work examines warfare throughout history, including human prehistory and the classical era, however the majority of his work concentrates on the 14th Century onwards to modern conflict of the 20th and 21st Centuries.

In A History of Warfare, Keegan outlines the development and limitations of warfare from prehistory to the modern era. It looks at various topics including the use of horses, logistics, and "fire". One key concept put forward is that war is inherently cultural. In the introduction, he rigourously denounces the idiom "war is a continuation of policy by other means", rejecting on its face "Clausewitzian" ideas.

He has also contributed to work on historiography in modern conflict.

Frank C. Mahncke wrote that Keegan is seen as being "among the most prominent and widely read military historians of the late twentieth century". In a book-cover blurb extracted from a more complex article, Michael Howard wrote: at once the most readable and the most original of living historians.

It should be noted that his book, Fields of Battle: The Wars for North America, which gives rather concise accounts of all the wars fought on the soil of North America, nevertheless contains something highly engaging: opening and closing essays that provide almost Tocquevillean insights into his own personal relationship to America.

An article in the Christian Science Monitor calls Keegan a "staunch supporter" of the Iraq war. The article quotes Keegan: "Uncomfortable as the "spectacle of raw military force" is, he concludes, that the Iraq war represents "a better guide to what needs to be done to secure the safety of our world than any amount of law-making or treaty-writing can offer." "

Keegan has also been criticised by peers, including Sir Michael Howard, Peter Paret and Christopher Bassford for his critical position on Carl von Clausewitz, a Prussian officer and writer on military philosophy. Keegan is described as profoundly mistaken and Bassford states that Nothing anywhere in Keegan's work—despite his many diatribes about Clausewitz and 'the Clausewitzians'—reflects any reading whatsoever of Clausewitz's own writings. He also caused some controversy by suggesting that General Sir Douglas Haig was an 'efficient and highly skilled soldier who did much to lead Britain to victory in the First World War'. This viewpoint may have been controversial at the time that he made it, but it is not now. Most serious modern historians such as Gary Sheffield, John Terraine, Gordon Corrigan and Richard Holmes would broadly agree.

* Barbarossa: Invasion of Russia, 1941 (New York, 1971) ISBN 0-345-02111-8 * The Face of Battle (London, 1976) ISBN 0-670-30432-8 * Six Armies in Normandy (1982) ISBN 0-14-005293-3 * The Mask of Command (London, 1987) ISBN 0-7126-6526-9 * The Price of Admiralty (1988) ISBN 0-09-173771-0 * Who Was Who In World War II (1978) ISBN 0-85368-182-1 * The Illustrated Face of Battle (New York and London: Viking, 1988) ISBN 0-670-82703-7 * The Second World War (Viking Press, 1990) ISBN 0-670-82359-7 * A History of Warfare (London, 1993) ISBN 0-679-73082-6 * Warpaths (Pimlico, 1996) ISBN 1-8441-3750-3 * The Battle for History: Refighting World War Two (Vintage), 1996) ISBN 0-679-76743-6 * Fields of Battle: The Wars for North America (1997) ISBN 0-679-74664-1 * War and Our World: The Reith Lectures 1998 (London: Pimlico, 1999) ISBN 0-375-70520-1 * The Book of War (ed.) (Viking Press, 1999) ISBN 0-670-88804-4 * The First World War (New York: Knopf, 1999) ISBN 0-375-40052-4 * Winston Churchill (2002) ISBN 0-670-03079-1 * Intelligence in War: Knowledge of the Enemy from Napoleon to Al-Qaeda (2003) ISBN 0-375-40053-2 * The Iraq War (2004) ISBN 0-09-180018-8

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*Snowman, Daniel "John Keegan" page 28–30 from History Today, Volume 50, Issue # 5, May 2000.