Chapter 2 surveys and analyzes the greatest ideas and theorists in war theory and strategy – including the philosophies of Sun Tzu, Thucydides, Machiavelli, Jomini, Clausewitz, Liddell Hart, and Mao. This chapter makes war theory and its recurring themes more accessible by presenting diverse perspectives spanning all eras of military thought from classical through the twentieth century. Each theorist’s background and main ideas are presented, and their strengths and weaknesses are summarized. As history’s preeminent but also most misunderstood war theorist, special attention is given Clausewitz. Principal themes include war’s fluidity, unpredictability, violence, and reciprocity; concentration and momentum; adaptability, intelligence, and relative capacity; military genius; centers of gravity and decisive points; fog, friction, chance, and policy; guerrilla, asymmetric, and nuclear warfare; and war’s moral and physical dimensions.