Following the outbreak of the Second World War, security policy in Britain was tightened. People from Nazi Germany (Germany and Austria) were classified as ‚enemy aliens'. Many of them were refugees, Jews or other persecuted people, but there was a fear of supporters, saboteurs or spies of the Nazi regime within the country.

Initially, people of German nationality were only registered and, depending on the security risk, had their rights restricted. However, following the German invasion of the Netherlands, Belgium, Luxembourg and France in the spring of 1940, a major wave of internment took place in Great Britain: all German males between 16 and 60 years of age were arrested and detained in special camps. Women were less systematically affected. When the internment camps in Great Britain became full, prisoners were also shipped to Canada and Australia in the summer of that same year to be held there. Shortly afterwards, the British government relaxed its internment policy again, and those detained were gradually released.

Other European and non-European countries also had provisions in their legislation regarding the treatment of nationals of enemy states. However, these provisions were not a reinvention from the Second World War, but built upon measures and laws from the First World War and earlier. Nevertheless, during the Second World War they were applied on an unprecedented scale.