This book talks about the mass displacement of civilians, estimated to be 14 to 15 million, in the twentieth-century Europe during the First World War. It looks at the causes and consequences of the refugee crisis and its aftermath, and the attempts to understand its significance. Key sites of displacement extended from Belgium to Armenia, taking in France, Italy, Austria-Hungary, East Prussia, the Russian Empire, Bulgaria, Greece, Turkey and Serbia. The German army's occupation of Belgium, France, Poland and Lithuania prompted the mass flight of refugees, as did Russia's invasion of East Prussia in 1914. Jewish, Ruthenian and Polish civilians in the Habsburg Empire fled their homes or were deported by the military to distant locations. Following Italy's attack on Austria-Hungary in May 1915, the Habsburg authorities ordered around 100,000 Slovenian subjects of the empire to leave. The Austrian and Bulgarian invasion of Serbia brought about a humanitarian catastrophe as civilians and the remnants of the Serbian army sought safety elsewhere. However, mass flight of civilian refugees did not begin in 1914 nor did it come to an end in 1918. Muslim refugees fled to the relative safety of Anatolia in order to escape violent persecution by Bulgarian and other forces during the Balkan Wars on 1912-13. There were complex movements of population between Greece, Bulgaria and Turkey before 1914. The complex process of repatriation and resettlement affected soldiers and civilians alike and rarely took place in stable or peaceful circumstances.