Forty-five years ago last Sunday, Vietnamese troops seized Phnom Penh and ended Cambodia's 45-month reign of terror known as the "killing fields." Under the leadership of Pol Pot, the Khmer Rouge government implemented policies—forced labor, resettlements, torture, starvation—that led to the death of 1.7-to-3 million people, or at least 20 percent of the nation's population. The regime destroyed the country, caused untold suffering, and left permanent scars. Painful as it is, we should not let these grim anniversaries go unremembered. For context, imagine a "political experiment" that obliterated our society and left a quarter of our 331-million population dead....