A Christian army led by the Polish High Duke Henry II the Pious, supported by the feudal nobility including Poles, Bavarian miners and military orders, was decisively defeated by the Mongols.

Backed by the nobility of Wrocław, Henry III forced the duke to cede central parts of Lower Silesia to him, while Bolesław himself retired to Legnica.

Furthermore, he came into conflict with his younger brother Konrad, who, originally predestined for an ecclesiastical career as Bishop of Passau, also demanded his distributive share and had to be paid off by Bolesław with the newly created Duchy of Głogów in 1251.

As after the death of Henry V in 1296, his eldest son Bolesław III the Generous was still a minor, King Wenceslaus took over his guardianship, strengthening the Bohemian influence in Silesia.

Even Bolesław's rule over Legnica was contested by his brother Władysław and in 1329 he had to pay homage to the Bohemian King John of Luxembourg to secure his reign.

Piast state from 1329 onwards became a Czech vassal, the political weakness of the duchy continued, caused by domestic conflicts between Bolesław's the Wastefull sons Wenceslaus and Louis the Fair strengthening the influences of the Bohemian monarchs.

The Protestant Reformation was introduced in the duchy as early as 1522, decisively promoted by the theologians Caspar Schwenckfeld and Valentin Krautwald, and the population quickly turned Lutheran.