In addition to preexisting threats such as the rise of China, the United States now faces a protracted struggle against Islamist terrorists. The military component of the nation’s security strategy requires a balanced force that can be employed across the spectrum of conflict. The Iraq War has shown the “1-4-2-1” force-sizing construct—maintaining a force able to defend the homeland, operate in and from four forward regions, simultaneously defeat two regional adversaries, and achieve a result such as regime change in one of them—to be unattainable. But by spending 4.5 percent of GDP on defense and with the right force mix, America will be able to lead coalitions against terrorists, restore order to unstable regions, do peacekeeping in regions of vital interest, deter aggression, and win a war if deterrence fails. The benefits of the resulting world order far outweigh the costs.