Vienna ( (listen) vee-EN-; German: Wien [vin] (listen); Austro-Bavarian: Wean [ven]) is the national capital, largest city, and one of nine states of Austria. Vienna is Austria's most populous city, with about two million inhabitants (2.9 million within the metropolitan area, nearly one third of the country's population), and its cultural, economic, and political center. It is the 6th-largest city proper by population in the European Union and the largest of all cities on Danube river.

Until the beginning of the 20th century, Vienna was the largest German-speaking city in the world, and before the splitting of the Austro-Hungarian Empire in World War I, the city had two million inhabitants. Today, it is the second-largest German-speaking city after Berlin. Vienna is host to many major international organizations, including the United Nations, OPEC and the OSCE. The city is located in the eastern part of Austria and is close to the borders of the Czech Republic, Slovakia and Hungary. These regions work together in a European Centrope border region. Along with nearby Bratislava, Vienna forms a metropolitan region with 3 million inhabitants. In 2001, the city center was designated a UNESCO World Heritage Site. In July 2017 it was moved to the list of World Heritage in Danger. Additionally, Vienna is known as the "City of Music" due to its musical legacy, as many famous classical musicians such as Beethoven and Mozart called Vienna home. Vienna is also said to be the "City of Dreams" because it was home to the world's first psychoanalyst, Sigmund Freud. Vienna's ancestral roots lie in early Celtic and Roman settlements that transformed into a Medieval and Baroque city. It is well known for having played a pivotal role as a leading European music center, from the age of Viennese Classicism through the early part of the 20th century. The historic center of Vienna is rich in architectural ensembles, including Baroque palaces and gardens, and the late-19th-century Ringstrae lined with grand buildings, monuments and parks.Vienna is known for its high quality of life. In a 2005 study of 127 world cities, the Economist Intelligence Unit ranked the city first (in a tie with Vancouver and San Francisco) for the world's most livable cities. Between 2011 and 2015, Vienna was ranked second, behind Melbourne. Monocle's 2015 "Quality of Life Survey" ranked Vienna second on a list of the top 25 cities in the world "to make a base within". Monocle's 2012 "Quality of Life Survey" ranked Vienna fourth on a list of the top 25 cities in the world "to make a base within" (up from sixth in 2011 and eighth in 2010). The UN-Habitat classified Vienna as the most prosperous city in the world in 20122013. The city was ranked 1st globally for its culture of innovation in 2007 and 2008, and sixth globally (out of 256 cities) in the 2014 Innovation Cities Index, which analyzed 162 indicators in covering three areas: culture, infrastructure, and markets. Vienna regularly hosts urban planning conferences and is often used as a case study by urban planners. Between 2005 and 2010, Vienna was the world's number-one destination for international congresses and conventions. It attracts over 6.8 million tourists a year.

The Soviet Union, officially the Union of Soviet Socialist Republics (USSR), was a communist state that spanned Eurasia from 1922 to 1991. It was nominally a federal union of multiple national republics; in practice its government and economy were highly centralized until its final years. The country was a one-party state (prior to 1990) governed by the Communist Party of the Soviet Union, with Moscow as its capital within its largest and most populous republic, the Russian SFSR. Other major urban centers were Leningrad (Russian SFSR), Kiev (Ukrainian SSR), Minsk (Byelorussian SSR), Tashkent (Uzbek SSR), Alma-Ata (Kazakh SSR) and Novosibirsk (Russian SFSR). It was the largest country in the world, covering over 22,402,200 square kilometres (8,649,500 sq mi), and spanning eleven time zones.

The Soviet Union had its roots in the October Revolution of 1917 when the Bolsheviks, headed by Vladimir Lenin, overthrew the Provisional Government that had earlier replaced the house of Romanov of the Russian Empire. They established the Russian Soviet Republic, the world's first constitutionally guaranteed socialist state. Tensions escalated into a civil war between the Bolshevik Red Army and many anti-Bolshevik forces across the former Empire, among whom the largest faction was the White Guard. The White Guard engaged in violent anti-communist repression against the Bolsheviks and suspected worker and peasant Bolsheviks known as the White Terror. The Red Army expanded and helped local Bolsheviks take power, establishing soviets, repressing their political opponents and rebellious peasants through Red Terror. By 1922, the balance of power had shifted and the Bolsheviks had emerged victorious, forming the Soviet Union with the unification of the Russian, Transcaucasian, Ukrainian and Byelorussian republics. Upon the conclusion of the civil war Lenin's government introduced the New Economic Policy, which led to a partial return of a free market and private property; this resulted in a period of economic recovery.

Following Lenin's death in 1924, Joseph Stalin came to power. Stalin suppressed all political opposition to his rule inside the Communist Party and inaugurated a command economy. As a result, the country underwent a period of rapid industrialization and forced collectivization, which led to significant economic growth, but also led to a man-made famine in 1932–1933. The Gulag labour camp system was also expanded in this period. Stalin also fomented political paranoia and conducted the Great Purge to remove his actual and perceived opponents from the Party through mass arrests of military leaders, Communist Party members, and ordinary citizens alike, who were then sent to correctional labor camps or sentenced to death.

On 23 August 1939, after unsuccessful efforts to form an anti-fascist alliance with Western powers, the Soviets signed a non-aggression pact with Nazi Germany. After the start of World War II, the formally neutral Soviets invaded and annexed territories of several Eastern European states, including the eastern regions of Poland, Lithuania, Latvia and Estonia. In June 1941 the Germans invaded, opening the largest and bloodiest theater of war in history. Soviet war casualties accounted for the majority of Allied casualties of the conflict in the process of acquiring the upper hand over Axis forces at intense battles such as Stalingrad. Soviet forces eventually captured Berlin and won World War II in Europe on 9 May 1945. The territory overtaken by the Red Army became satellite states of the Eastern Bloc. The Cold War emerged in 1947, where the Eastern Bloc confronted the Western Bloc, which would unite in the North Atlantic Treaty Organization in 1949.

Following Stalin's death in 1953, a period known as de-Stalinization and the Khrushchev Thaw occurred under the leadership of Nikita Khrushchev. The country developed rapidly, as millions of peasants were moved into industrialized cities. The USSR took an early lead in the Space Race with the first ever satellite and the first human spaceflight and the first probe to land on another planet, Venus. In the 1970s, there was a brief détente of relations with the United States, but tensions resumed when the Soviet Union deployed troops in Afghanistan in 1979. The war drained economic resources and was matched by an escalation of American military aid to Mujahideen fighters.

In the mid-1980s, the last Soviet leader, Mikhail Gorbachev, sought to further reform and liberalize the economy through his policies of glasnost and perestroika. The goal was to preserve the Communist Party while reversing economic stagnation. The Cold War ended during his tenure and in 1989, Warsaw Pact countries in Central and Eastern Europe overthrew their respective Marxist-Leninist regimes. Strong nationalist and separatist movements broke out across the USSR. Gorbachev initiated a referendum—boycotted by Lithuania, Latvia, Estonia, Armenia, Georgia, and Moldova — which resulted in the majority of participating citizens voting in favor of preserving the Union as a renewed federation. In August 1991, a coup d'état was attempted by Communist Party hardliners. It failed, with Russian President Boris Yeltsin playing a high-profile role in facing down the coup. The main result was the banning of the Communist Party. The republics, led by Russia and Ukraine, declared independence. On 25 December 1991, Gorbachev resigned. All the republics emerged from the dissolution of the Soviet Union as independent post-Soviet states. The Russian Federation (formerly the Russian SFSR) assumed the Soviet Union's rights and obligations and is recognized as its continued legal personality in world affairs.

The Soviet Union produced many significant social and technological achievements and innovations regarding military power. It boasted the world's second-largest economy and the largest standing military in the world. The USSR was recognized as one of the five nuclear weapons states. It was a founding permanent member of the United Nations Security Council as well as a member of the OSCE, the WFTU and the leading member of the Council for Mutual Economic Assistance and the Warsaw Pact.

Before its dissolution, the USSR had maintained its status as a superpower, alongside the United States, for four decades after World War II. Sometimes also called "Soviet Empire", it exercised its hegemony in East-Central Europe and worldwide with military and economic strength, proxy conflicts and influence in developing countries and funding of scientific research, especially in space technology and weaponry.