In august 1914, the people of europe were swept into the first of the wars that would make this century the bloodiest ever. Seventy million soldiers from more than twenty countries marched off enthusiastically to do their duty. In Killing Fields, soldiers from all sides remember the trenches and the tactics - and the terrible nature and scale of the slaughter that shattered the old world order. In the end, four empires collapsed and nine million gave their lives. Some would become ardent pacifists while others were determined to seek retribution - and many would find themselves fighting another war only two decades later. DVD only. 56 minutes. WGBH.