In the Treaty of Versailles, after the defeat of Germany and Austria-Hungary in World War I, the population of Upper Silesia was to hold a plebiscite to determine the division of the province between Poland and Germany, with the exception of a 333 km2 (129 sq mi) area around Hlučín (Hultschiner Ländchen), which was granted to Czechoslovakia in 1920 despite its German-speaking majority.
That was not accepted by the Big Four, however, and British Prime Minister David Lloyd George successfully suggested for a plebiscite to be organised.
A new partition plan was prepared by the League of Nations and was adopted by the Conference of Ambassadors, the successor of the Supreme Council of the Principal Allied Powers, on 20 October 1921.
In 1921, a convention in Geneva to regulate the conditions in Upper Silesia took place under the chairmanship of Felix Calonder, a member of the Swiss Federal Council.
The conference had the aims of alleviating the economic consequences of the partition of the highly-industrialised region and guaranteeing minority rights in both Polish and German Upper Silesia.
Germany had to accept the loss of its coal-bearing land and was left with the economically-unimportant West Upper Silesia although Silesian coal was then highly relevant to the German economy.
The Upper Silesian Mixed Commission (or "Mixed Commission for Upper Silesia"), composed of an equal number of Polish and German delegates and headed by a neutral Swiss president, Felix Calonder, was set up as a quasi-judicial body to arbitrate disputes for a 15-year interim period until 1937.