Some historians maintain that the area was inhabited by the Silingae, a Vandal tribe, from the 3d cent. B.C. to the 3d cent. A.D. Slavic tribes settled here c.A.D. 500, and Silesia was an integral part of Poland by the 11th cent. King Boleslaus III (reigned 1102–38), of the Piast dynasty, divided Poland into four hereditary duchies (of which Silesia was one) for the benefit of his sons. After 1200 the duchy of Silesia fell apart into numerous minor principalities.
The Silesian Piasts encouraged German colonization of their lands, the larger part of which became thoroughly Germanized, and in the early 14th cent. the Silesian princes accepted the king of Bohemia as their suzerain and thus became mediate princes of the Holy Roman Empire. During the Hussite Wars of the 15th cent. Silesia, with Moravia, was temporarily detached from the Bohemian crown and was ruled by Hungary. In 1490, however, both Silesia and Moravia reverted to Bohemia, with which they passed to the house of Hapsburg in 1526.
Hapsburg rule and increasing Germanization loosened Silesia's historic ties with Poland. However, the ducal title, along with several fiefs, remained with the Silesian branch of the Piast dynasty until the extinction of the line in 1675. The margraviate of Jägerndorf was purchased in 1523 by a cadet branch of the Hohenzollern dynasty of Brandenburg, which later also claimed inheritance to other Silesian fiefs. Elector Joachim II of Brandenburg, moreover, concluded (1537) an alliance with the Piast duke, by which Brandenburg would inherit the Piast principalities if the Piast dynasty became extinct. This treaty was declared invalid by King Ferdinand I of Bohemia (later Emperor Ferdinand I). In 1621, John George of Jägerndorf, brother of the elector of Brandenburg, lost his fief for having supported Frederick the Winter King.
The Thirty Years War (1618–48) brought untold misery to Silesia under successive Saxon, imperial, and Swedish occupation. It reverted to Austrian control at the Peace of Westphalia (1648). In 1675, on the death of the last Piast, Austria incorporated the Piast territories into the Bohemian crown domain. The Counter Reformation had by then made great progress in Silesia, although Lutheranism was tolerated in Breslau (Wrocław) and certain other districts.
It was on the very shaky dynastic grounds indicated above that Frederick II of Prussia, as heir of the house of Brandenburg, claimed a portion of Silesia in 1740 from Maria Theresa, who had just assumed the succession to Austria, Bohemia, and Hungary. His claim and his offer to assist Maria Theresa in the impending War of the Austrian Succession were rejected by the queen while Prussian troops were already invading Silesia. The Silesian Wars (1740–42 and 1744–45) were part of the general War of the Austrian Succession. By the Treaty of Berlin (1742), Maria Theresa ceded all of Silesia except Teschen and present Czech Silesia to Prussia; this cession was ratified by the Treaty of Dresden (1745). In the Seven Years War, Prussia retained Silesia.
During the Industrial Revolution of the late 18th and 19th cent. textile weaving and coal mining developed rapidly in Silesia, but industrialization brought great social tension. The Silesian weavers became dependent on entrepreneurs who farmed out work; working conditions and unemployment became intolerable, and discontent ran high. Most coal mining was in the hands of private industry, under which miners were often mistreated. Landholding conditions also were iniquitous, most of the land being held by owners of large estates. The resulting tensions assumed an ethnic character, since the upper and middle classes were predominantly German, while a large percentage of the workers were Polish. Though these conditions were gradually improved, Silesia even in the 20th cent. remained, despite its great productivity, a relatively backward area.
After World War I the Treaty of Versailles (1919) provided for a plebiscite to determine if Upper Silesia was to remain German or to pass to Poland. The results of the plebiscite (1921) were favorable to Germany except in the easternmost part of Upper Silesia, where the Polish population predominated. After an armed rising of the Poles (1922) the League of Nations accepted a partition of the territory; the larger part of the industrial district, including Katowice, passed to Poland. The contested city and district of Teschen were partitioned in 1920 between Poland and Czechoslovakia (to the satisfaction of neither) by the conference of ambassadors. The political division of the Silesian industrial district was carried out so arbitrarily that the boundaries often cut through mines; some workers slept in one country and worked in another. As a result of the Munich Pact of 1938 most of Czech Silesia was partitioned between Germany and Poland, and after the German conquest of Poland in 1939 all Polish Silesia was annexed to Germany.
After World War II the pre-1938 boundaries were restored, but all formerly Prussian Silesia E of the Lusatian Neisse was placed under Polish administration (a small section of Lower Silesia W of the Neisse was incorporated with the East German state of Saxony). The Allies also allowed the expulsion (in an "orderly and humane" manner) of the German population from Czech Silesia, Polish Silesia, and Polish-administered Silesia. The mass expulsion of Germans was, perforce, neither orderly nor humane; moreover, although the transfer of territories to Polish administration was made subject to revision in a final peace treaty with Germany, the Polish government treated all Silesia as integral Polish territory. West Germany finally relinquished all claims to the area under the terms of a nonaggression pact with Poland in 1972. With the unification of East and West Germany in 1990, German leaders attempted once again to allay the fears of its neighbors, particularly Poland, by declaring the stability of the borders determined at the end of World War II.