Since 1920, when Cieszyn Silesia was divided, it has been one of the most important industrial centers of Czechoslovakia. TŽ was nationalized in 1946 and its development continued during the Communist era, when heavy industry was very important. It is the largest steel mill in the country and still has a major impact on the industrial town of Třinec and surrounding areas, on its character, demographics and air pollution, although the latter significantly decreased since the fall of communism in 1989.