The division of Cieszyn in July 1920 brought enormous changes to both parts of the town. Cieszyn residents fled the town in great numbers to Austria and Germany, their places being taken by newcomers from Poland or Czechoslovakia. The hard process of integration with new national states awaited both parts of the previously single town, as did the building of new economic links almost from scratch. Cieszyn numbered over fifteen thousand in 1921 and in 1938 eighteen and a half. It took many years before an infrastructure independent of Český Těąín was constructed. It was not until the second half of the 1930s that Cieszyn began to develop again. New connections were gradually built, chiefly with the rest of the Province of Silesia which Cieszyn belonged to from 1922 onwards, partly thanks to the railway to Zebrzydowice which was built in 1934.
       On the other hand most of the previously joint municipal utilities were in Poland which eased the process of taking over government in Cieszyn by the new Polish institutions. After 1922 the elected Town Council, with a preponderance of Poles held power, although the interests of the German minority were respected. Poles, Germans and Jews co-operated together for the good of the town, which now found itself in a difficult situation.
       The part of Cieszyn on the other side of the Olza, the former industrial district of the town, experienced considerably greater changes. In less than twenty years Český Těąín was transformed into a town with full civic rights, and all the essential structures, buildings and infrastructure, new schools and a new town hall which was opened in 1929. The number of dwellings in the town doubled, and the population rose from eight thousand in 1921 to ten and a half in 1931. Most self-declared Germans lived here, and the numbers of Czechs and Poles grew in the inter-war years. Mayor Józef Kożdoń led the local authority. Český Těąín was an important centre for the Polish minority, with Polish schools and the most important Polish organisations located there. The people of both towns were active, and in each over 150 different associations functioned.
       After the Zaolzie region was annexed to Poland in October 1938 the two parts of the town were united and the local authority was based in the Town Hall in Český Těąín, now referred to as West Cieszyn. The town remained united during the Second World War when Cieszyn was incorporated into the Third Reich. All the important political positions were assumed by representatives of the Reich. Non-Germans suffered numerous forms of discrimination, many Poles were executed publicly; for example in Pod Wałką in 1942. Jews were deported to concentration camps where most of them perished, and Jewish synagogues and houses of prayer were destroyed. After the war Cieszyn reverted to its status of 1937.

J. Spyra, transl. D. French