Silesia is rich in mineral and natural resources and includes several important industrial areas. Silesia's largest city and historical capital is Wrocław. Other large cities are Opole (Oppeln), Gliwice (Gleiwitz), and Katowice (Kattowitz) in Poland; Ostrava and Opava in the Czech Republic; and Görlitz in Germany. Its main river is the Oder (Odra).
Silesia's borders and national affiliation have changed radically over time, both when it was a hereditary possession of noble houses and after the rise of modern nation-states. The first known states to hold power there were those of Greater Moravia at end of 9th century and Bohemia early in the 10th century. In the 10th century Silesia was incorporated into the early Polish state, but it later broke into independent duchies, coming under increasing Czech and German influence. It came under the rule of the Crown of Bohemia, which passed to the Austrian Habsburg Monarchy in 1526. Most of Silesia was conquered by Prussia in 1742, later becoming part of the German Empire, the Weimar Republic and Nazi Germany up to 1945. After World War I the easternmost part of this region was awarded to Poland by the victorious Allies after rebellions by Silesian Polish people and a plebiscite. After World War II the bulk of Silesia was transferred to Polish jurisdiction and became part of Poland. The remaining parts of Silesia went to Czechoslovakia after World War I, and are part of the Czech Republic with the part west of the Oder-Neisse line in Germany.
Most inhabitants of Silesia today speak the national languages of their respective countries (Polish, Czech, German). There is an ongoing debate whether a local Silesian speech should be considered a Polish dialect or a separate language. There also exists a Silesian German or Lower Silesian language, although this form of German is almost extinct.
Silesia has historically been an ethnically diverse region. In the fourth century BC Celts entered Silesia, settling around Mount Ślęża near modern Wrocław, Oława, and Strzelin. Germanic tribes were first recorded within Silesia in the first century. Slavic peoples arrived in the region around the seventh century, and by the early ninth century their settlements had stabilized. Local Slavs started to erect boundary structures like the Silesian Przesieka and the Silesia Walls. The eastern border of Silesian settlement was situated to the west of the Bytom, and east from Racibórz and Cieszyn. East of this line dwelled a closely related Slav tribe, the Vistulans. Their northern border was in the valley of the Barycz river, north of which lived the Polans.
The first known states in Silesia were Greater Moravia and Bohemia. In the tenth century, the Polish ruler Mieszko I of the Piast dynasty incorporated Silesia into the Polish state. During the Fragmentation of Poland, Silesia, as well as the rest of the country, was divided among many independent duchies ruled by various Silesian dukes. During this time, German cultural and ethnic influence increased as a result of immigration from German-speaking parts of the Holy Roman Empire. In 1178, parts of the Duchy of Kraków around Bytom, Oświęcim, Chrzanów and Siewierz were transferred to the Silesian Piasts, although their population was primarily Vistulan and not of Silesian descent.
Between 1289 and 1292 Bohemian king Wenceslaus II became suzerain of some of the Upper Silesian duchies. It wasn't until 1335, however, that Polish kings renounced their hereditary rights to Silesia. The province became part of the Bohemian Crown under the Holy Roman Empire, and passed with that crown to the Habsburg Monarchy of Austria in 1526.
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, even though it was a part of the Diocese of Kraków. The Duchy of Crossen 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.
In 1742, most of Silesia was seized by King Frederick the Great of Prussia in the War of the Austrian Succession, becoming the Prussian Province of Silesia; consequently, Silesia became part of the German Empire when it was proclaimed in 1871.
After World War I, 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), although most of Cieszyn and territory to the east of it went to Poland (see Zaolzie).
Polish Silesia was among the first regions invaded during Germany's 1939 attack on Poland. One of the goals of Nazi occupation, particularly the occupation of Upper Silesia, was to expel the Polish Silesian population. German repatriation of Poles in Upper Silesia was made a priority for two crucial reasons. First, Nazi Germany was resentful over the loss of Silesia after the uprisings of the early 1920s and wished to regain the region for its natural resource wealth and strategically important locomotive network. Second, the Nazi war machine needed more members. Those repatriated as German were immediately subject to military service, thus bolstering the German Army's numbers. As for the non-German speaking Polish population of Silesia, they were reduced to a lower worker class status and were oftentimes severely mistreated by their new German overlords. This treatment would be addressed by the Poles years later.
In 1945, Silesia and its population went through another traumatic change. The German expulsion of Poles from Silesia was echoed by Polish expulsion of Germans. The Potsdam Conference of 1945 concluded that the Oder-Neisse would be the official border between Germany and Poland. Millions of German Silesians were evicted from their homes and replaced by Poles from the East. Furthermore, the newly formed Polish United Workers' Party created a Ministry of the Recovered Territories that claimed half of the available arable land for state-run collectivized farms. Many Silesian residents not only resented the Germans for their invasion in 1939, but now also the newly formed Polish communist government for their population shifting and interference in agricultural, as well as industrial, affairs.
The administrative division of Silesia within Poland has changed several times since 1945. Since 1999 it has been divided between Lower Silesian Voivodeship, Opole Voivodeship, Silesian Voivodeship and Lubusz Voivodeship. Czech Silesia is now part of the Czech Republic, forming the Moravian-Silesian Region and the northern part of the Olomouc Region. Germany retains the Silesia-Lusatia region (Niederschlesien-Oberlausitz or Schlesische Oberlausitz) west of the Neisse, which is part of the federal state of Saxony.