The 20th Century has witnessed state-sponsored carnage on an unprecedented scale. What made this era so susceptible to Hitler’s “Final Solution,” Stalin’s Gulag, Mao’s “Great Leap Forward,” Pol Pot’s killing fields, and other atrocities? Does the answer lie in the rogue ideologies that found acceptance among society’s intellectual elites—“isms” that elevated the dictates of the State over the rights of the individual and the institutions of civil society? Celebrated historian Robert Conquest discusses the rise of these ideologies—and how to protect the 21st Century from their destructive grip.