This picture shows the handing out of Dannebrog, the Danish flag, to people in the city of Flensburg during the days running up to a referendum on 20 March 1920. They were voting for either German or Danish rule, and 75% voted in favour of German.
As a result of the Second Schleswig War (1864) Denmark had been forced to surrender the Duchies of Schleswig and Holstein. This meant that large numbers of Danish-minded residents in north Schleswig (now Sønderjylland and of which Flensburg is the main city) were forced to live under German rule.
At the end of World War One the Treaty of Versailles (Art 109) stated that plebiscites, or referendums, should be held in Schleswig to determine the future nationality of the region. The referendums were an opportunity for every member of an electorate to cast their vote on a single issue, usually of national or international relevance. The general assumption in Denmark was that people of the northern part, Zone 1 (Sønderjylland), would vote in favour of Danish nationality while the results from the southern provinces, Zone 2, remained to be seen. Most people were likely to vote German, but the self-contained city of Flensburg could turn out in favour of Denmark.
The fight for votes in Flensburg became cutthroat. During the days leading up to the vote streets were filled with Danish, German and regional Schleswig-Holstein flags, and posters were seen everywhere in an attempt to influence voters.