Title: Eastern Bloc
Content:  structure of the "Polish region." Soviet authorities immediately started a campaign of sovietization of the newly Soviet-annexed areas. Soviet authorities collectivized agriculture, and nationalized and redistributed private and state-owned Polish property. Initial Soviet occupations of the Baltic countries had occurred in mid-June 1940, when Soviet NKVD troops raided border posts in Lithuania, Estonia and Latvia, followed by the liquidation of state administrations and replacement by Soviet cadres. Elections for parliament and other offices were held with single candidates listed and the official results fabricated, purporting pro-Soviet candidates' approval by 92.8 percent of the voters in Estonia, 97.6 percent in Latvia, and 99.2 percent in Lithuania. The fraudulently installed peoples assemblies immediately requested admission into the USSR, which was granted 
Title: Baltic states
Content:  of the Baltic countries were controlled by the Russian Empire until the final stages of World War I in 1918, when Estonia, Latvia and Lithuania gained their sovereignty. The three countries were independent until the outbreak of World War II. In 1940, all three countries were invaded, occupied and annexed by the Stalinist Soviet Union. In 1941 followed the invasion and occupation Lithuania, Latvia and Estonia by Nazi Germany, before the Red Army reinvaded in 1944–1945 and the Soviet Union was able to regain control over the three countries until 1991. Soviet rule ended in the Baltic countries in 1989–1991 as the newly elected parliaments of the three nations declared the Soviet occupation illegal, culminating with the full restoration of the independence of the three countries in August 1991.
Title: Sovietization of the Baltic states
Content:  The Sovietization of the Baltic states refers to the sovietization of all spheres of life in Estonia, Latvia and Lithuania when they were under control of the Soviet Union. The first period deals with the occupation from June 1940 to July 1941 when the German occupation began. The second period covers 1944 when the Soviet forces pushed the German out, until 1991 when independence was declared.
Title: Soviet economic blockade of Lithuania
Content:  Shortly after Germany and the Soviet Union signed of the Ribbentrop-Molotov Pact in 1939, the Baltic states had been occupied and illegally incorporated into the Soviet Union; the territories, including Lithuania, fell under control of USSR after World War II. Despite being part of the Soviet Union for more than 40 years, in the 1980s the Baltic states were still seen as somewhat different from the rest of the USSR. After Mikhail Gorbachev was elected leader of the Communist Party of the Soviet Union (CPSU) in 1985, the Soviet government gradually introduced some liberalization measures, including perestroika and glasnost. These efforts caused massive 
Title: Belarus
Content:  In 1939, Nazi Germany and the Soviet Union invaded and occupied Poland, marking the beginning of World War II. The Soviets invaded and annexed much of eastern Poland, which had been part of the country since the Peace of Riga two decades earlier. Much of the northern section of this area was added to the Byelorussian SSR, and now constitutes West Belarus. The Soviet-controlled Byelorussian People's Council officially took control of the territories, whose populations consisted of a mixture of Poles, Ukrainians, Belarusians and Jews, on 28 October 1939 in Białystok. Nazi Germany invaded the Soviet Union in 1941. The defense of Brest Fortress was the first major battle of Operation Barbarossa. The Byelorussian SSR was the hardest-hit Soviet republic in World War II; it remained in Nazi hands until 1944. The German Generalplan Ost called for the extermination, expulsion, or enslavement of most or all Belarusians 
Title: History of the Soviet Union (1927–1953)
Content:  In the aftermath of World War II, the Soviet Union extended its political and military influence over Eastern Europe, in a move that was seen by some as a continuation of the older policies of the Russian Empire. Some territories that had been lost by Soviet Russia in the Treaty of Brest-Litovsk (1918) were annexed by the Soviet Union after World War II: the Baltic states and eastern portions of interwar Poland. The Russian SFSR also gained the northern half of East Prussia (Kaliningrad Oblast) from Germany. The Ukrainian SSR gained Transcarpathia (as Zakarpattia Oblast) from Czechoslovakia, and Ukrainian populated Northern Bukovina (as Chernivtsi Oblast) from Romania. Finally, by the late 1940s, pro-Soviet 
Title: Soviet involvement in regime change
Content:  The Soviet Union occupied the Baltic states under the auspices of the 1939 Molotov–Ribbentrop Pact in June 1940. They were then incorporated into the Soviet Union as constituent republics in August 1940, though most Western powers never recognized their incorporation. On 22 June 1941, Nazi Germany attacked the Soviet Union and, within weeks, occupied the Baltic territories. In July 1941, the Third Reich incorporated the Baltic territory into its Reichskommissariat Ostland. As a result of the Red Army's Baltic Offensive of 1944, the Soviet Union recaptured most of the Baltic states and trapped the remaining German forces in the Courland pocket 
Title: Soviet involvement in regime change
Content:  hundreds of thousands of people from eastern Poland to Siberia and other remote parts of the Soviet Union in four major waves of deportation between 1939 and 1941. Soviet forces occupied eastern Poland until the summer of 1941, when they were driven out by the German army in the course of Operation Barbarossa. The area was under German occupation until the Red Army reconquered it in the summer of 1944. An agreement at the Yalta Conference permitted the Soviet Union to annex almost all of their Molotov–Ribbentrop Pact portion of the Second Polish Republic, compensating the Polish People's Republic with the southern half 
Title: Polish–Soviet War
Content:  state in 1990. Under the Lithuanian Soviet Socialist Republic, Vilnius became a city dominated by ethnic Lithuanians. After the Soviet invasion of Poland of September 1939, the partition of Belarus and Ukraine ended on Soviet terms. After Operation Barbarossa and occupation by Nazi Germany, the Soviet Union returned in 1944 and the two Soviet republics permanently reclaimed what had been Polish "Kresy" from 1920 to 1939. Since the post-World War II adjustments, the borders of the republics had remained stable, except for the 1954 transfer of Crimea from the Russian SFSR to the Ukrainian SSR. The Soviet republics' borders had been preserved as borders of independent Belarus 
Title: Baltic states under Soviet rule (1944–1991)
Content:  This Baltic states were under Soviet rule from the end of World War II in 1945, from Sovietization onwards until independence was regained in 1991. The Baltic states were occupied and annexed, becoming the Soviet socialist republics of Estonia, Latvia and Lithuania. After their annexation by Nazi Germany, the USSR reoccupied the Baltic territories in 1944 and maintained control there until the Baltic states regained their independence nearly 50 years later in the aftermath of the Soviet coup of 1991.

Question: when did the soviet union first gain control of parts of poland and the baltic republics?
Answer: 14 June 1940.