After World War I, plebiscites were supposed to be one of the factors determining the shape of the borders of the Second Polish Republic, e.g., borders between Poland and Czechoslovakia with respect to Cieszyn Silesia. During this period, there was a Polish–Czech–German conflict over the affiliation of this region. Despite the agreement of November 5, 1918, on the ethnic division of Cieszyn Silesia, which was favourable for Poland, an armed intervention took place, and most of the area was occupied by the Czechs. Therefore, the Paris Peace Conference decided to take the area under international supervision and then carry out a plebiscite. During the plebiscite, Polish authorities realised that Czechoslovakia could win the vote. It was decided to postpone the plebiscite and suggest arbitration. Finally, during the Polish-Bolshevik war, the unfavourable for Poland division of Cieszyn Silesia was decided upon at the Spa conference of August 28, 1920.