Bohemian Crown to the Habsburg monarchy. In the 15th century, several changes were made to Silesia's borders. Parts of the territories which had been transferred to the Silesian Piasts in 1178 were bought by the Polish kings in the second half of the 15th century (the Duchy of Oświęcim in 1457; the Duchy of Zator in 1494). The Bytom area remained in the possession of the Silesian Piasts, though it was a part of the Diocese of Kraków. The Duchy of Krosno Odrzańskie () was inherited by the Margraviate of Brandenburg in 1476, and with the renunciation of King Ferdinand I and the estates of Bohemia in 1538, became an integral part of Brandenburg. From 1645 until 1666, the Duchy of Opole and Racibórz was held in pawn by the Polish House of Vasa as dowry of the Polish queen Cecylia Renata. In 1742, most of Silesia was seized by King Frederick the Great of Prussia in the War of the Austrian Succession, eventually becoming the Prussian Province of Silesia in 1815; consequently, Silesia became part of the German Empire when it was proclaimed in 1871. After World War I, a part of Silesia, Upper Silesia, was contested by Germany and the newly independent Second Polish Republic. The League of Nations organized a plebiscite to decide the issue in 1921. It resulted in 60% of votes being cast for Germany and 40% for Poland. Following the third Silesian uprising (1921), however, the easternmost portion of Upper Silesia (including Katowice), with a majority ethnic Polish population, was awarded to Poland, becoming the Silesian Voivodeship. The Prussian Province of Silesia within Germany was then divided into the provinces of Lower Silesia and Upper Silesia. Meanwhile, Austrian Silesia, the small portion of Silesia retained by Austria after the Silesian Wars, was mostly awarded to the new Czechoslovakia (becoming known as Czech Silesia and Zaolzie), although most of Cieszyn and territory to the east of it went to Poland. Polish Silesia was among the first regions invaded during Germany's 1939 attack on Poland, which started World War II. One of the claimed goals of Nazi German occupation, particularly in Upper Silesia, was the extermination of those whom Nazis viewed as "subhuman", namely Jews and ethnic Poles. The Polish and Jewish population of the then Polish part of Silesia was subjected to genocide involving expulsions, mass murder and deportation to Nazi concentration camps and forced