I'm re-reading the following:

Carl Schmitt, The Concept of the Political. A work which, to quote Nietzsche, counts as a timely untimely meditation. I am surprised that strategists do not read it if only for its clear emphasis on the necessity and meaning of disntinguishing between friend and enemy.

John Buchan, Greenmantle. A work of fiction which, IMO, contains more words of wisdom than will be found in your average, bog standard, academic tome. Set during WWI it revolves around the fortunes of a group of British intelligence officers and their attempt to thwart German plans in the Ottoman Empire. Along the way one gets the best disection of the Middle Eastern mentality and the Mind of Islam you're likely to find; 'No one knows what will set off a jihad!'. Much of it may be politically incorrect but that simply adds to its truth value.

Hegel, The Philosophy of Right (especially section 445)

Shimon Naveh, In Pursuit of Military Excellence: The Evolution of Operational Theory. I first read this during my undergraduate studies and, like most fresh faced and easily impressed layabouts, was bowled over by his verbose and self-important proclamations. Though still a valuable study of the development and conceptual foundations of Soviet/Russian deep operations theory (if anything this is its saving grace) I am not surprised that the IDF found his recent theory of SOD (Systematic Operational Design) so hard to digest that they spat it out in favour of a more traditional emphasis on "actual" military art in their recent Gaza campaign which paid dividends.