During the depths of the Cold War, a macabre logic caused the U.S. and Soviet Union to become locked in an arms race, ultimately amassing enough nuclear weapons to end civilization many times over. Both sides would have liked to deescalate. But for decades, neither could trust that the other would comply with any arms reduction treaty. By the 1980s, however, scientists had developed seismographs, satellites, and tamper-proof cameras. Now that each side could monitor the other, disarmament took