The history of Poland from 1945 to 1989 spans the period of Marxist–Leninist regime in Poland after the end of World War II. These years, while featuring general industrialization, urbanization and many improvements in the standard of living, were marred by early Stalinist repressions, social unrest, political strife and severe economic difficulties. Near the end of World War II, the advancing Soviet Red Army, along with the Polish Armed Forces in the East, pushed out the Nazi German forces from occupied Poland. In February 1945, the Yalta Conference sanctioned the formation of a provisional government of Poland from a compromise coalition, until postwar elections. Joseph Stalin, the leader of the Soviet Union, manipulated the implementation of that ruling. A practically communist-controlled Provisional Government of National Unity was formed in Warsaw by ignoring the Polish government-in-exile based in London since 1940. During the subsequent Potsdam Conference in July–August 1945, the three major Allies ratified the colossal westerly shift of the Polish frontier and approved its new territory between the Oder–Neisse line and Curzon Line, which resulted in the Polish borders shrinking and resembling those of the former Piast dynasty era. Following the destruction of the Polish-Jewish population in the Holocaust, the flight and expulsion of Germans in the west, resettlement of Ukrainians in the east, and the expulsion and resettlement of Poles from the Eastern Borderlands (Kresy), Poland became for the first time in its history an ethnically homogeneous nation-state without prominent minorities. The new government solidified its political power, while the Polish United Workers' Party (PZPR) under Bolesław Bierut gained firm control over the country, which would remain an independent state within the Soviet sphere of influence. The July Constitution was promulgated on 22 July 1952 and the country officially became the Polish People's Republic (PRL). Following Stalin's death in 1953, a political "thaw" allowed a more liberal faction of the Polish communists, led by Władysław Gomułka, to gain power. By the mid-1960s, Poland began experiencing increasing economic as well as political difficulties. They culminated in the 1968 Polish political crisis and the 1970 Polish protests when a consumer price hike led to a wave of strikes. The government introduced a new economic program based on large-scale loans from western creditors, which resulted in a rise in living standards and expectations, but the program meant growing integration of Poland's economy with the world economy and it faltered after the 1973