During the First World War, Woodrow Wilson, the American President, outlined a new principle for drawing up national borders, which he termed ‘the people’s right of self-determination’. In October 1918, the German government adopted this principle for a reorganisation of the country’s borders, thus paving the way for a referendum in Schleswig.

On 16 – 17 November 1918, immediately after the cessation of hostilities, representatives of the pro-Danish population of North Schleswig attended a meeting in Aabenraa under the leadership of H.P. Hanssen, who was a member of the German parliament. At this meeting, it was decided to demand that North Schleswig be permitted to vote en bloc, while separate, municipal votes could be held in the neighbouring regions of Central Schleswig.

This demand received the backing of the Danish government and was accepted at the Versailles peace conference in 1919. Under the watchful eye of international observers, two referendums were held in 1920, one on 10 February in North Schleswig (Zone 1) and the other on 14 March in Central Schleswig (Zone 2). A proposal for a referendum in the southernmost part of Schleswig (Zone 3) was rejected.