The Duchy of Courland and Semigallia (Latin: Ducatus Curlandiæ et Semigalliæ; German: Herzogtum Kurland und Semgallen; Latvian: Kurzemes un Zemgales hercogiste; Lithuanian: Kuršo ir Žiemgalos kunigaikštystė; Polish: Księstwo Kurlandii i Semigalii) was a duchy in the Baltic region, then known as Livonia, that existed from 1561 to 1569 as a nominally vassal state of the Grand Duchy of Lithuania and subsequently made part of the Crown of the Polish Kingdom from 1569 to 1726 and incorporated into the Polish–Lithuanian Commonwealth in 1726. On March 28, 1795, it was annexed by the Russian Empire in the Third Partition of Poland. There was also a short-lived wartime state existing from March 8 to September 22, 1918, with the same name. Plans for it to become part of the United Baltic Duchy, subject to the German Empire, were thwarted by Germany's surrender of the Baltic region at the end of the First World War. The area became a part of Latvia at the end of World War I.

Duchy of Courland and Semigallia - Wikipedia