For generations, among those who revere the work of Carl von Clausewitz, the role of his beloved wife, née Marie von Brühl, in shaping his seminal work on military theory has been a subject of intense speculation. It seems certain that without her On War would never have been published. But as historian and Clausewitz scholar Vanya Eftimova Bellinger establishes in this ground-breaking biography of the "other" Clausewitz, Marie was far more than merely a supportive wife who facilitated her husband's legacy. Marie's 1810 marriage to von Clausewitz did not make sense by most accounts (least of all to her mother). She was a wealthy, cultured, and politically engaged young woman; he was a minor Prussian officer. But the bond between Marie and Claus was forged by love, a deep sense of trust, and a meeting of the minds over common interests. A newly discovered archive of correspondence reveals the extent of Marie's influence on her husband, beginning with the very early days of the courtship and lasting until his premature death. The two came to a "collaborative opinion" on many topics, from the moral implications of war to the emotional constitution of true leadership. Marie's involvement, too, adds insight about the role of class and gender relations in a time when women were excluded from politics-the perspective of a spouse and caretaker on the home-front, observing the physical and emotional effects of combat. The issues that Marie von Clausewitz raised about the hardships of war - such as the social isolation and treatment of veterans, and the use of violence to achieve political and economic rights - still resonate today. This biography sheds light on an extraordinary life and mind, offering the first comprehensive and compelling look at the woman behind the composition of On War.