West Prussia, Ger. Westpreussen, former province of Prussia, 9,867 sq mi (25,556 sq km), NE Germany, extending S from the Baltic Sea, between Pomerania on the west and East Prussia on the east. Danzig was the capital. The larger part of the region belonged to Poland until the Polish partitions of 1772 and 1793 and included Pomerelia (Ger. Pommerellen; see Pomerania). The province also included, prior to World War I, the western portion of originally East Prussian territory, including the cities of Elbing, Marienburg, and Marienwerder. The Treaty of Versailles (1919) gave most of West Prussia to Poland (see Polish Corridor) and made Danzig and its environs a free city. The remainder of West Prussia was divided between the Prussian province of Grenzmark Posen-West Prussia and the district of West Prussia, incorporated with the province of East Prussia. The whole territory was again annexed to Germany at the outbreak (1939) of World War II, but in 1945 the Potsdam Conference placed it under Polish administration, where it has remained since.