On the 30th of April, 1975, the world's eyes were fixed on Saigon. After three decades of bitter civil war, Vietnam's struggle for independence finally seemed to be coming to an end. Peace, however, would remain elusive. Over the next fifteen years, the country would be compelled to dislodge the Khmer Rouge regime from Cambodia, bringing to an end one of the worst genocides in modern history. In episode one of this two-part series, Christopher Bardsley sifts through the convoluted causes of this poorly understood war, and uncovers the story of those who were forced to intervene.