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.
Congress Poland
The Kingdom of Poland, informally known as Congress Poland or Russian Poland, was created in 1815 by the Congress of Vienna as a sovereign state of the Russian partition of Poland. Connected until 1832 by personal union with the Russian Empire under the Constitution of the Kingdom of Poland, it was gradually thereafter integrated politically into Russia over the course of the 19th century, made an official part of the Russian Empire in 1867, and finally replaced during World War I by the Central Powers in 1915 with the nominal Regency Kingdom of Poland.