The referendums in Europe in the wake of the First World War were the result of a political doctrine of self-determination and the idea that nations are clearly defined units created on the basis of shared history and language.
Referendums were therefore only held in regions where defeated countries bordered new or neutral nations. The victors were not interested in referendums.
France and Italy took over Alsace-Lothringen and the Southern Tyrol, respectively, without consulting the local populations – and Romania did the same with Transylvania.
In addition to the votes in Schleswig, four referendums were held under international observation in the period 1920 – 21.
Two between Germany and Poland (one in Eastern Prussia in 1920 and one in Upper Silesia in 1921), one between Austria and Yugoslavia (in Carinthia in 1920), and one between Austria and Hungary (in Burgenland in 1921).
In addition, a number of referendums were held without international observation, including those in Vorarlberg and Salzburg (between Austria and Germany), on the Åland Islands (between Sweden and Finland) and in Vilnius (between Poland and Lithuania).