After World War I, Lower Silesia, having by far a German majority, remained with Germany while Upper Silesia, after a series of insurrections by the Polish inhabitants, was split. Part joined the Second Polish Republic and was administered as the Silesian Voivodeship. The Prussian Province of Silesia within Germany was divided into the Provinces of Lower Silesia and Upper Silesia. Austrian Silesia (officially: Duchy of Upper and Lower Silesia; almost identical with modern-day Czech Silesia), the small portion of Silesia retained by Austria after the Silesian Wars, became part of the new Czechoslovakia. During the Second World War, Nazi Germany invaded Polish parts of Upper Silesia. Jews were subject to genocide in the Holocaust, while German plans towards Poles involved ethnic cleansing and biological extermination.