What is Realpolitik? How did the concept come about, and what does it stand for? This book explores the origins and meaning of a core precept of international history and politics. Statesmen, diplomats, and analysts alike deploy the term as if it were a timeless label. Endlessly, they suppose, states compete with each other for power in a zero-sum game. Yet Realpolitik was born in Germany in the mid-nineteenth century. The circumstances of its birth are key to its meaning. Realpolitik emerged among Europe's constitutional struggles on the one hand, and the wars of Italian and German unification on the other. Revolutionary disappointment, the end of the Romantic era, and the rise of a new scientific materialism all informed a Realist period of political strongmen. Rather than describing a permanent state of things, this book suggests, Realpolitik is rooted in nineteenth-century European and German politics, and consequently the rise of an aggressive nationalism.