Now, this is a great and timely book. To give a short synopsis, Howard Caygill does two major moves. The first one is to offer a challenging re-reading of Clausewitz' super-influential book, On War, arguing, that it brings a set of alternatives to Fichte, Schelling and Hegel into Kantian philosophy insofar as it stresses the physics of war and resistance. In a sense, On War can thus be called On Resistance as that, which conditions war is the capacity to resist. Not stable, not inexhaustible, quite fungid. Just holding an ontological primacy. Something Caygill also identifies with a Clausewitz's contemporary, the painter Francesco Goya, as supporting the argument by the idea that resistance is 'in' the game.
The second move is a kind of chronological look, or, better said, a sketchy conceptual history, through the ways, how Clausewitz and the idea of resistance bound with his thought have informed different ways of thinking resistance (and revolution), from Marx and Engels, Lenin, Rosa Luxemburg through Mao, Gandhi, through the French resistance and de Gaulle, Emmanuel Levinas, Pier Paolo Passolini, the Situationists, the Zapatistas, the Naxalites in India, or the authors of The Coming Insurrection to Julian Assange and other more or less expected examples. Here, the book indeed holds to its sub-title, which is A Philosophy of Defiance and instead of telling the reader to think this or that way, takes all the examples as building up to a body of thought.
The only minor criticism of this book might be that it is perhaps 'too' generous toward almost every single idea it engages with, but then, levying this as an objection would be an act of counter-resistance. By the end of the book, every careful reader would be perfectly cautious there.