Kingdom of Poland (1917–1918)

The Kingdom of Poland (Polish: Królestwo Polskie, German: Königreich Polen), also known informally as the Regency Kingdom of Poland (Polish: Królestwo Regencyjne), was a short-lived puppet state of the German Empire and polity that was proclaimed during World War I by it and Austria-Hungary on 5 November 1916 on the territories of formerly Russian-ruled Congress Poland held by the Central Powers as the Government General of Warsaw and which became active on 14 January 1917. It was subsequently transformed between 7 October 1918 and 22 November 1918 into the independent Second Polish Republic, the customary ceremonial founding date of the latter being set at 11 November 1918.

Source: Wikipedia — Kingdom of Poland (1917–1918) (CC BY-SA 4.0)