Such a large growth in population was owing to an industrial development within the district luring a large influx of migrant workers, mostly from western Galicia. Traditionally the area in most parts was inhabited by Silesian Lachs speaking Cieszyn Silesian dialect. After World War I and fall of Austria-Hungary the region of Cieszyn Silesia including the territory of Freistadt political district became disputed land between Czechoslovakia and Poland. This led to Polish–Czechoslovak War and the division of the region and district on 28 July 1920, by a decision of the Spa Conference. Majority of the municipalities became a part of Czechoslovakia (with the district being afterwards known as "Okres Fryštát") and only the easternmost municipalities became a part of Poland, and were then transferred to Cieszyn County.