In peacetime, Rosen finds, innovation has been the product of analysis and the politics of military promotion, in a process that has slowly but successfully built military capabilities critical to American military success. In wartime, by contrast, innovation has been constrained by the fog of war and the urgency of combat needs. Rosen draws his principal evidence from U.S. military policy between 1905 and 1960, though he also discusses the British army's experience with the battle tank during World War I.