After the First World War, a territorial dispute between Poland and Czechoslovakia erupted over Teschen, a region containing iron and textile works, crucial railway lines, and most importantly, a sizable portion of the Silesian coalfields.
Following the fall of Austria-Hungary, Poland and Czechoslovakia reached an agreement on a frontier line on November 5, 1918; however, neither country upheld the agreement. The Poles announced on December 10, 1918 that elections to the Warsaw Diet would be held in Teschen on January 26th. This was followed by the Polish mobilization of troops along the frontier line on the 17th of December, and a Czech ultimatum (January 23, 1919) for their removal. During the short military confrontation which began on January 23rd, the Czechs gained the advantage, and this phase ended in an armistice on February 5th.
Both governments presented their case to the Paris Peace Conference and its Commission on the Teschen dispute. At the end of April 1919, the Commission advised the two states to settle the matter between themselves, and negotiations were held at Cracow from July 23rd to July 30th. The Czechs refused the Polish demand for a plebiscite, and the Supreme Council began arbitration in September 1919. On September 27th, the Supreme Council decided plebiscites would be held in Teschen under the control of a Plebiscite Commission.
Tensions continued unabated. The plebiscite region was placed under martial law in March 1920 and again on May 19, 1920, following a riot in Teschen. On June 25th, the Council of Ambassadors proposed the substitution of arbitration for the plebiscite. After receiving information from all parties involved, the Council of Ambassadors drafted a declaration delineating the boundaries of Polish and Czech Teschen, which the two governments signed on July 28, 1920.