Most of Silesia was annexed by the King of Prussia under the Treaty of Berlin in 1742. Only the Duchy of Teschen, the Duchy of Troppau and the Duchy of Nysa remained under the control of the Bohemian crown and as such were known as the Duchy of Upper and Lower Silesia until 1918.
In 1742, King of Prussia acquired most of Silesia through the Treaty of Berlin. The remaining territories, including Teschen, Troppau, and Nysa, continued to be under Bohemian rule and were referred to as Upper and Lower Silesia until 1918.