Towards the beginning of this massive biography, Short cautions readers against dismissing the terror of Pol Pot's regime as the incomprehensible work of evil men. Instead, Short argues, the explanations for the Khmer Rouge regime, which resulted in the death of over one-fifth of Cambodia's population, or 1.5 million people, are ""rooted in history."" The book begins its search for these explanations in the early life of Saloth Sar, a ""mediocre student"" whose political disengagement offered no hint of the ideological nightmare he would fashion under the name Pol Pot. As a student in Paris, Sar's political philosophy slowly began to take shape, and the book deftly follows his political evolution abroad as a part of the ""Cercle Marxiste"" against the backdrop of the tumultuous history of Cambodia after the war. Short, a former BBC correspondent who has also written an acclaimed biography of Mao Zedong, moves between Sar's personal story and the broader history with ease. By the time these two narratives converge in the lucid and harrowing description of the Khmer Rouge victory and subsequent evacuation of Phnom Penh city, the book has already laid the groundwork for the horrors that would follow. Occasionally, Short's attempts to understand Pol's psychology lapse into vast over-generalization, as when he attributes Pol's erratic behavior to ""the perpetual Khmer tendency to take things to extremes."" More often, though, Short expertly identifies the historical and ideological causes that generated the Khmer Rouge impulse to terror and that eventually led to the regime's collapse. Though daunting in length, Short's book offers a copiously well-researched and surprisingly accessible portrait of Pol that will prove indispensable to anyone interested in the subject.