Karl Baedeker. Great Britain: Handbook for Travellers. Old House, 2013 . As I said, I'm a sucker for facsimile editions, and this one has many nice foldout maps. As the cover doesn't fail to tell you, this is the version supposedly used by the Luftwaffe to plan the Baedeker raids. At any rate, if you were time-travelling back to 1937 Britain and could only take one book, you could take this, but really it would be a waste of luggage allowance because you could buy it when you got there.
Daniel Pick. War Machine: The Rationalisation of Slaughter in the Modern Age. New Haven and London: Yale University Press, 1993. One of those books I've seen referenced many times but never seen. Looks at the increasing appetite for destruction from the 19th century through to the First World War -- Clausewitz, 1870, the Channel Tunnel all get a look-in. May get a bit psychohistorical at times.
David Reynolds. The Long Shadow: The Great War and the Twentieth Century. London: Simon & Schuster, 2013. Did somebody say 'upcoming centenary of the First World War'? Probably, since the centenary of the the First World War is upcoming. Reynolds usually works on the Second World War period, but that probably makes him a good choice for this contribution to the literature, a reflection upon the effects of the war on the rest of the century, in terms of big themes like war and peace (obviously), democracy, empire and so on.