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.
Polish United Workers' Party
The Polish United Workers' Party was established at the unification congress of the Polish Workers' Party (PPR) and Polish Socialist Party (PPS) during meetings held from 15 to 21 December 1948. The unification was possible because the PPS activists who opposed unification (or rather absorption into the Workers' Party) had been forced out of the party. Similarly, the members of the PPR who were accused of "rightist – nationalistic deviation" were expelled. Thus, for all intents and purposes, the PUWP was the PPR under a new name.