World War I marked a rupture in Europe’s recent experience of refugees. During the German invasion of Belgium, massacres of thousands of civilians and the destruction of buildings led to an exodus of more than a million people. Almost a quarter of them came to England, where the British government had offered "victims of war the hospitality of the British nation". Most Belgian refugees returned to Belgium at the end of World War I despite having having been able to assimilate smoothly in the UK.

Belgium was not the only refugee crisis to emerge from World War I. After Austria-Hungary declared war on, and subsequently invaded Serbia, tens of thousands of Serbians were forced to leave their homes.

Some of the largest atrocities committed during and after World War I were directed at the Armenians. The population of 2 million was decimated by what was later recognised as the first genocide of the 20th century. Systematic persecution under the Ottoman empire meant that half of that population were dead by 1918 and hundreds of thousands were homeless and stateless refugees. Today, the Armenian diaspora is around 5 million in number, while there are just 3.3 million in what is today the republic of Armenia.