Some years—1789, 1929, 1989—change the world suddenly. Or do they? In 2020, a pandemic converged with an economic collapse, inequalities exploded, and institutions weakened. Yet these crises sprang not from new risks but from known dangers. The world—like many patients—met 2020 with a host of preexisting conditions, which together tilted the odds toward disaster. Perhaps 2020 wasn’t the year the world changed; perhaps it was simply the moment the world finally understood its deadly diagnos...