In this tense climate it was decided that a plebiscite would be held in the area asking its people which country the territory should join. Plebiscite commissioners arrived there at the end of January 1920 and after analysing the situation declared a state of emergency in the territory on 19 May 1920. The situation in the territory remained very tense. Mutual intimidation, acts of terror, beatings and even killings affected the area.Zahradnik 1992, 62-63. A plebiscite could not be held in this atmosphere. On 10 July both sides renounced the idea of plebiscite and entrusted the Conference of Ambassadors with the decision.Zahradnik 1992, 64. Eventually 58.1% of the area of Cieszyn Silesia, along with 67.9% of the population, was taken over by Czechoslovakia on 28 July 1920 by decision of the Spa Conference. This decision divided a historically unified region, leaving a sizeable Polish minority in Czechoslovakia and in practice created Trans-Olza, the eastern part of the Czech part of Cieszyn Silesia delimited by the Olza River. The division of 1920 had an immediate impact on the life of the region. Many families were divided by the new border. Several municipalities were divided between the two states—Cieszyn (PL) / Český Těšín (CS), Leszna Górna (PL) / Horní Líštná (CS), and Marklowice Górne (PL) / Dolní Marklovice (CS), to name a few.
