Warfare today is a mixture of ancient principles and modern realities. Military planners must consider a bewildering range of conventional and emerging threats—everything from the actions of rival nations, to terror networks, cyber-attacks, eroding international treaties, and even climate change. In this complex and fraught security environment, the United States faces no shortage of potential flashpoints as it seeks to defend its global interests. How, then, can the nation avoid war? And if it is drawn into armed conflict, what weapons, tactics, and strategic principles will help the US win?