Question: When did the country where Piltene is located become part of the USSR?

full_context: Document 1: Molotov–Ribbentrop Pact: In mid-June 1940, when international attention was focused on the German invasion of France, Soviet NKVD troops raided border posts in Lithuania, Estonia and Latvia. State administrations were liquidated and replaced by Soviet cadres, in which 34,250 Latvians, 75,000 Lithuanians and almost 60,000 Estonians were deported or killed. Elections were held with single pro-Soviet candidates listed for many positions, with resulting peoples assemblies immediately requesting admission into the USSR, which was granted by the Soviet Union. The USSR annexed the whole of Lithuania, including the Scheschupe area, which was to be given to Germany.
Document 2: Estonia: On 6 August 1940, Estonia was annexed by the Soviet Union as the Estonian SSR. The provisions in the Estonian constitution requiring a popular referendum to decide on joining a supra-national body were ignored. Instead the vote to join the Soviet Union was taken by those elected in the elections held the previous month. Additionally those who had failed to do their "political duty" of voting Estonia into the USSR, specifically those who had failed to have their passports stamped for voting, were condemned to death by Soviet tribunals. The repressions followed with the mass deportations carried out by the Soviets in Estonia on 14 June 1941. Many of the country's political and intellectual leaders were killed or deported to remote areas of the USSR by the Soviet authorities in 1940–1941. Repressive actions were also taken against thousands of ordinary people.
Document 3: History of Latvia: The First Latvian National Awakening began in the 1850s and continued to bear fruit after World War I when, after two years of struggle in the Latvian War of Independence, Latvia finally won sovereign independence, as recognised by Soviet Russia in 1920 and by the international community in 1921. The Constitution of Latvia was adopted in 1922. Political instability and effects of the Great Depression led to the May 15, 1934 coup d'état by Prime Minister Kārlis Ulmanis. Latvia's independence was interrupted in June -- July 1940, when the country was occupied and incorporated into the Soviet Union. In 1941 it was invaded and occupied by Nazi Germany, then reconquered by the Soviets in 1944 -- 45.
Document 4: Post-Soviet states: The post-Soviet states, also collectively known as the former Soviet Union (FSU) or former Soviet Republics, are the 15 independent states that emerged from the Union of Soviet Socialist Republics in its dissolution in December 1991, with Russia internationally recognised as the successor state to the Soviet Union. On March 11, 1990, Lithuania was the first to declare its independence, with Estonia and Latvia following suit in August 1991. All three Baltic states claimed continuity from the original states that existed prior to their annexation by the Soviet Union in 1944 and were admitted to the United Nations on 17 September 1991. The remaining 12 republics all subsequently seceded. 12 of the 15 states, excluding the Baltic states, initially formed the CIS and most joined CSTO, while the Baltic states focused on European Union and NATO membership.
Document 5: Grobiņa Castle: Grobiņa Castle is a medieval castle located in the town of Grobiņa, Latvia, in western Courland. The ancient Curonian castle hill ("Skābāržu kalns") is located only 100 m from the castle. It is supposed to be the famous Seeburg, which is mentioned in Scandinavian sources as early as the 9th century.
Document 6: Rēzekne Castle: Rēzekne Castle ruins are located in the centre of Rēzekne, Latvia, a city in the centre of Latgale. The castle served as a base of the local Livonian order landlords until the 16th century and also as the main military support base for battles against Russians and Lithuanians. Today, fragments of the stone walls and the foundation can be seen on the ancient castle hill.
Document 7: Gothic architecture: The Palais des Papes in Avignon is the best complete large royal palace, alongside the Royal palace of Olite, built during the 13th and 14th centuries for the kings of Navarre. The Malbork Castle built for the master of the Teutonic order is an example of Brick Gothic architecture. Partial survivals of former royal residences include the Doge's Palace of Venice, the Palau de la Generalitat in Barcelona, built in the 15th century for the kings of Aragon, or the famous Conciergerie, former palace of the kings of France, in Paris.
Document 8: Piltene Castle: Piltene Castle is a Bishopric of Courland castle in the town of Piltene in the historical region of Courland, in western Latvia. Until the 16th century it served as a capital of Bishopric of Courland.
Document 9: Estonia: In 1989, during the "Singing Revolution", in a landmark demonstration for more independence, more than two million people formed a human chain stretching through Lithuania, Latvia and Estonia, called the Baltic Way. All three nations had similar experiences of occupation and similar aspirations for regaining independence. The Estonian Sovereignty Declaration was issued on 16 November 1988. On 20 August 1991, Estonia declared formal independence during the Soviet military coup attempt in Moscow, reconstituting the pre-1940 state. The Soviet Union recognised the independence of Estonia on 6 September 1991. The first country to diplomatically recognise Estonia's reclaimed independence was Iceland. The last units of the Russian army left on 31 August 1994.
Document 10: Kalmar: From the thirteenth to the seventeenth centuries, Kalmar was one of Sweden's most important cities. Between 1602 and 1913 it was the episcopal see of Kalmar Diocese, with a bishop, and the Kalmar Cathedral from 1702 is still a fine example of classicistic architecture. It became a fortified city, with the Kalmar Castle as the center. After the Treaty of Roskilde in 1658, Kalmar's importance diminished, until the industry sector was initiated in the 19th century. The city is home to parts of Linnaeus University.
Document 11: Dissolution of the Soviet Union: On June 14, 1987, about 5,000 people gathered again at Freedom Monument in Riga, and laid flowers to commemorate the anniversary of Stalin's mass deportation of Latvians in 1941. This was the first large demonstration in the Baltic republics to commemorate the anniversary of an event contrary to official Soviet history. The authorities did not crack down on demonstrators, which encouraged more and larger demonstrations throughout the Baltic States. The next major anniversary after the August 23 Molotov Pact demonstration was on November 18, the date of Latvia’s independence in 1918. On November 18, 1987, hundreds of police and civilian militiamen cordoned off the central square to prevent any demonstration at Freedom Monument, but thousands lined the streets of Riga in silent protest regardless.
Document 12: Raseborg Castle: The first written data about the castle is from 1378. Its main purpose was to protect Sweden's interests in southern Finland against the Hanseatic city of Tallinn. The castle was originally built on a small island in the north end of a sea bay. The historians think that the castle was built in 3 different stages over time from the 14th to the 16th century.
Document 13: Chlemoutsi: It was built in the early 1220s by the Crusader rulers of the Principality of Achaea as their main stronghold, and is perhaps the finest fortification of the early period of Frankish rule in Greece preserved in the country today. The castle is located on a small plateau above sea level, and comprises a central hexagonal keep, built around an inner courtyard and containing two-storeyed halls along its entire length, and complemented by an outer wall enclosing an outer yard on its western side. The castle is largely preserved in its original 13th-century state, with only minor later modifications for the installation of artillery.
Document 14: Latvian Soviet Socialist Republic: Following the Welles Declaration of July 23, 1940, the annexation of Latvia into the Soviet Union (USSR) on 5 August 1940 was not recognized as legitimate by the United States, the European Community, and recognition of it as the nominal fifteenth constituent republic of the USSR was withheld for five decades. Its territory was subsequently conquered by Nazi Germany in June -- July 1941, before being retaken by the Soviets in 1944 -- 1945. Nevertheless, Latvia continued to exist as a de jure independent country with a number of countries continued to recognize Latvian diplomats and consuls who still functioned in the name of their former governments.
Document 15: Kaliningrad: In the Middle Ages it was the site of the Old Prussian settlement Twangste. In 1255, during the Northern Crusades, a new fortress named Königsberg was built by the Teutonic Knights, a German Catholic religious order of crusaders. Königsberg became the capital of the Duchy of Prussia and later of East Prussia in the German Empire. It was heavily damaged during World War II, and its population had to flee or were removed by force. Königsberg became a Russian city, was repopulated with ethnic Russians and renamed "Kaliningrad" in 1946. At the 2010 Census, Kaliningrad's population was 431,902.
ground_truth: 5 August 1940
sub_queries: Piltene >> country Answer: Latvia
when did Latvia become part of the soviet union Answer: 5 August 1940