Book excerpt: War at the Speed of Light describes the revolutionary and ever-increasing role of directed-energy weapons (such as laser, microwave, electromagnetic pulse, and cyberspace weapons) in warfare. Louis A. Del Monte delineates the threat that such weapons pose to disrupting the doctrine of Mutually Assured Destruction, which has kept the major powers of the world from engaging in nuclear warfare. Potential U.S. adversaries, such as China and Russia, are developing hypersonic missiles and using swarming tactics as a means to defeat the U.S. military. In response, the U.S. Department of Defense established the 2018 National Security Strategy, emphasizing directed-energy weapons, which project devastation at the speed of light and are capable of destroying hypersonic missiles and enemy drones and missile swarms. Del Monte analyzes how modern warfare is changing in three fundamental ways: the pace of war is quickening, the rate at which weapons project devastation is reaching the speed of light, and cyberspace is now officially a battlefield. In this acceleration of combat called "hyperwar," Del Monte shows how disturbingly close the world is to losing any deterrence to nuclear warfare.