Short answers, pulled from the story.
John Desmond Patrick Keegan was born in Clapham, London on the 15th of May 1934. He moved to Somerset during the evacuation that followed the outbreak of the Second World War while he was still a child.
John Keegan took up a lectureship in military history at the Royal Military Academy Sandhurst in 1960 and remained there for 26 years becoming a senior lecturer in military history. During this tenure he held a visiting professorship at Princeton University and served as Delmas Distinguished Professor of History at Vassar College in the United States.
The condition rendered him unfit for military service later in life after he contracted orthopaedic tuberculosis at age 13 which affected his gait and left him with long-term physical effects. The timing of his birth made him too young for war service anyway when the Second World War broke out.
John Keegan stated I will never oppose the Vietnam War because Americans were right to do it even though they fought it in wrong way but still a correct war. An article in The Christian Science Monitor called Keegan staunch supporter of Iraq War where he concluded Iraq war represents better guide to what needs done to secure safety of world than any amount law-making or treaty-writing can offer.
On the 29th of June 1991 Keegan appointed Officer of Order British Empire OBE in recognition service within operations Gulf. In 2000 New Year Honours he knighted for services to Military History and was elected Fellow Royal Society Literature FRSL in 1986 before winning Duff Cooper Prize in 1993.