History of Poland
The Polish People's Republic ("Polska Rzeczpospolita Ludowa") was established under the rule of the communist Polish United Workers' Party (PZPR). The name change from the Polish Republic was not officially adopted, however, until the proclamation of the Constitution of the Polish People's Republic in 1952.
Vistula Land
As the Russians retreated, the Central Powers occupied the area (1915); subsequently they proposed the establishment of the Kingdom of Poland (1916–1918). In the March 1918 Treaty of Brest-Litovsk, Russia (by then embroiled in a civil war), effectively ceded all Polish territories it had formerly possessed to the German Empire and Austria-Hungary.a Sources agree that after the fall of the January Uprising in 1864, the autonomy of Congress Poland was drastically reduced. However, they disagree on whether the state of the Kingdom of Poland (colloquially known as Congress Poland) was officially replaced by the Vistula land as a province of the Russian Empire, as many sources still use the term Congress Poland for the post-1864 period. The sources are also unclear as to when the Kingdom of Poland (or Vistula land) officially ceased to exist; some argue it ended with the assumption of control by the German and Austro-Hungarian occupying authorities; others, that it ended with the proclamation of the Regency Kingdom of Poland in 1916; finally, some argue that it occurred only with the creation of the independent Second Polish Republic in 1918. Examples: