The Soviet Union, officially the Union of Soviet Socialist Republics (USSR), was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen national republics; in practice, both its government and its economy were highly centralized until its final years. It was a one-party state governed by the Communist Party of the Soviet Union, with the city of Moscow serving as its capital as well as that of its largest and most populous republic: the Russian SFSR. Other major cities included 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 country's roots lay in the October Revolution of 1917, when the Bolsheviks, under the leadership of Vladimir Lenin, overthrew the Russian Provisional Government that had earlier replaced the House of Romanov of the Russian Empire. The Bolshevik victory established the Russian Soviet Republic, the world's first constitutionally guaranteed socialist state. Persisting internal tensions escalated into the Russian Civil War. By 1922 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, the partial return of a free market and private property.

Following Lenin's death in 1924, Joseph Stalin came to power. Stalin inaugurated a period of rapid industrialization and forced collectivization that led to significant economic growth, but also contributed to a famine in 19301933 that killed millions. The labour camp system of the Gulag was also expanded in this period. Stalin conducted the Great Purge to remove his actual and perceived opponents. Hundreds of thousands were executed. On 23 August 1939, the Soviets signed the MolotovRibbentrop Pact with Nazi Germany, which established an understanding of neutrality and non-aggression between the two sides. With the outbreak of World War II following the German invasion of Poland, the formally neutral Soviet Union invaded and annexed the territories of several states in Eastern Europe. In June 1941, Germany broke the non-aggression pact and launched a large-scale invasion of the Soviet Union. Despite initial German successes, the Soviets gained the upper hand over Axis forces at the Battle of Stalingrad and eventually captured Berlin. The combined Soviet civilian and military casualty countestimated to be around 27 million peopleaccounted for the majority of losses of Allied forces. In the aftermath of World War II, the territory taken by the Red Army formed various Soviet satellite states.

The beginning of the Cold War saw the Eastern Bloc of the Soviet Union confront the Western Bloc of the United States, with the latter grouping becoming largely united in 1949 under the North Atlantic Treaty Organization and the former grouping becoming largely united in 1955 under the Warsaw Pact. Following Stalin's death in 1953, a period known as de-Stalinization occurred under the leadership of Nikita Khrushchev. The Soviets took an early lead in the Space Race with the first artificial satellite, the first human spaceflight, and the first probe to land on another planet (Venus). In the 1970s, there was a brief dtente in the Soviet Union's relationship with the United States, but tensions resumed following the Soviet invasion of Afghanistan in 1979. In the mid-1980s, the last Soviet leader, Mikhail Gorbachev, sought to reform the country through his policies of glasnost and perestroika. In 1989, during the closing stages of the Cold War, various countries of the Warsaw Pact overthrew their MarxistLeninist regimes, which was accompanied by the outbreak of strong nationalist and separatist movements across the entire Soviet Union. In 1991, Gorbachev initiated a national referendumboycotted by the Soviet republics of Lithuania, Latvia, Estonia, Armenia, Georgia, and Moldovathat resulted in the majority of participating citizens voting in favour of preserving the country as a renewed federation. In August 1991, hardline members of the Communist Party staged a coup d'tat against Gorbachev; the attempt failed, with Boris Yeltsin playing a high-profile role in facing down the unrest, and the Communist Party was subsequently banned. The Soviet republics, led by Russia and Ukraine, formally declared independence. On 25 December 1991, Gorbachev resigned from his presidency. All of the republics emerged from the dissolution of the Soviet Union as fully independent post-Soviet states. Above the other former republics, the Russian Federation (formerly the Russian SFSR) assumed the Soviet Union's rights and obligations and has since remained recognized as its successor legal personality in international affairs.

The Soviet Union produced many significant social and technological achievements and innovations, particularly with regard to military power. It boasted the world's second-largest economy, and the Soviet Armed Forces comprised the largest standing military in the world. An NPT-designated state, it possessed the largest arsenal of nuclear weapons in the world. It was a founding member of the United Nations as well as one of the five permanent members of the United Nations Security Council; it was also a member of the OSCE and the WFTU, and the leading member of the Council for Mutual Economic Assistance. Between the end of World War II in 1945 and its dissolution in 1991, the Soviet Union had maintained its status as one of two superpowers vis--vis the United States. It was sometimes referred to informally as the "Soviet Empire" in relation to its exercising of hegemony across Europe as well as worldwide with a combination of military and economic strength; proxy conflicts and influence in the Third World; and funding of scientific research, especially in space technology and weaponry.

Belarus, officially the Republic of Belarus, and historically Byelorussia, is a landlocked country in Eastern Europe. It is bordered by Russia to the east and northeast, Ukraine to the south, Poland to the west, and Lithuania and Latvia to the northwest. Covering an area of 207,600 square kilometres (80,200 sq mi) and with a population of 9.3 million, Belarus is the 13th-largest and the 20th-most populous country in Europe. The country is administratively divided into seven regions. Minsk is the capital and largest city.

Until the 20th century, different states at various times controlled the lands of modern-day Belarus, including Kievan Rus', the Principality of Polotsk, the Grand Duchy of Lithuania, the Polish–Lithuanian Commonwealth, and the Russian Empire. In the aftermath of the Russian Revolution in 1917, different states arose competing for legitimacy amidst the Civil War, ultimately ending in the rise of the Byelorussian SSR, which became a founding constituent republic of the Soviet Union in 1922. After the Polish-Soviet War, Belarus lost almost half of its territory to Poland. Much of the borders of Belarus took their modern shape in 1939, when some lands of the Second Polish Republic were reintegrated into it after the Soviet invasion of Poland, and were finalized after World War II. During World War II, military operations devastated Belarus, which lost about a quarter of its population and half of its economic resources. The republic was redeveloped in the post-war years. In 1945, the Byelorussian SSR became a founding member of the United Nations, along with the Soviet Union.

The parliament of the republic proclaimed the sovereignty of Belarus on 27 July 1990, and during the dissolution of the Soviet Union, Belarus declared independence on 25 August 1991. Following the adoption of a new constitution in 1994, Alexander Lukashenko was elected Belarus's first president in the country's first and only free election post-independence, serving as president ever since. Lukashenko heads an authoritarian government with a poor human rights record due to widespread abuses. Lukashenko has continued a number of Soviet-era policies, such as state ownership of large sections of the economy. Belarus is the only country in Europe officially using the death penalty. In 2000, Belarus and Russia signed a treaty for greater cooperation, forming the Union State.

Belarus is a developing country, ranking 53rd in the Human Development Index. It has been a member of the United Nations since its founding and has joined the CIS, the CSTO, the EAEU, the OSCE, and the Non-Aligned Movement. It has shown no aspirations of joining the European Union but nevertheless maintains a bilateral relationship with the bloc and also participates in two EU projects, the Baku Initiative and the Eastern Partnership. Belarus suspended its participation in the latter on 28 June 2021, after the EU imposed more sanctions against the country.