After four years of fighting, 20 million soldiers and civilians dead, and three collapsed empires, World War One ended and a new world order emerged. But the armistice held only temporarily and the promise to end all wars was repeatedly broken over the last 100 years. Charlie Sennott has been tracing how this war is the source of so many modern conflicts, many of them he’s covered as a correspondent over the last three decades. We look at the circumstances that led to that war, and how those circumstances are eerily similar to today.