For 70 years, the thinking inside the Pentagon was that only nations with nuclear weapons could threaten America’s existence. But that assumption is now in doubt: in a world in which almost everything is interconnected – phones, cars, electrical grids, and satellites – everything can be disrupted, if not destroyed. In THE PERFECT WEAPON, Belfer Center Senior Fellow and Adjunct Lecturer in Public Policy David Sanger, the New York Times national security correspondent, details how this new revolution, being conducted largely in secret, is reshaping global power.

Iran’s top nuclear negotiator was heading back to Tehran on Sunday to consult with his nation’s leadership, as negotiators remained divided over how to limit and monitor Tehran’s nuclear program and even on how to interpret the preliminary agreement they reached two months ago.