Background and the course of events
From the end of the war in November 1918 until January 1919, there was hectic political activity to end armed conflicts between various nations – conflicts related to the definition of borders and territorial matters in general.
However, it was not possible to establish unequivocal boundaries for all states, and therefore it was laid down in the Treaty of Versailles in 1919 that plebiscites under the supervision of international commissions should be held in five regions of Europe in the course of 1920-21. The first of these was held in Schleswig in February and March.
The campaign leading up to the plebiscite in Upper Silesia took place at almost the same time as in Schleswig, but was much more violent. On account of its natural resources and well-developed industry, Upper Silesia was much coveted by both Germany and Poland. At the referendum on 20 March 1920, there were 706,993 votes for Germany and 479,349 for Poland, but neither party was satisfied. In the end, the allied powers determined a partition of Upper Silesia: the major part of the coal mining and industrial areas and the iron ore deposits went to Poland. Only the western part, which was mostly agricultural, remained in German hands
The third plebiscite took place 11 July 1920 in a small area of West and East Prussia. 105,071 votes were cast, 98 % for East Prussia.
The fourth plebiscite took place in Carinthia in October 1920, and in this case the choice was between Austria and the newly-formed state of Yugoslavia. The lead up to the actual referendum was plagued by violent conflict between the two sides, but when the votes were cast there was a considerable majority for Austria, even in areas with a majority of Slovenian speaking inhabitants. The border drawn in 1919 was therefore not altered.
The last of the European plebiscites under international control was held at the end of 1921 in Burgenland, also called German Western Hungary. In this case the choice was between Austrian and Hungarian citizenship. There was a clear majority in favour of Hungary, so the area remained under Hungarian jurisdiction.
The borders established by the plebiscites in Schleswig, Carinthia and Burgenland are still in force.
The borders established by the plebiscites in West and East Prussia as well as Silesia were altered after World War II when the Soviet Union took over East Prussia and Poland was moved further west. There were no plebiscites in this connection.
In The Saarland, a plebiscite was held in 1935 according to the Treaty of Versailles, and a large majority voted for Germany. The plebiscite was repeated in 1955 with the same result.
The plebiscites held after World War I were the outcome of the modern idea that nations are clear-cut communities determined by history, language and culture. The plebiscites offered the populations involved a clear choice between two possibilities: German or Polish? Austrian or Hungarian? In fact, though, border areas are often multilingual and multicultural, so plebiscites can return unexpected results.