Short answers, pulled from the story.
The Soviet Union existed from 1922 until its dissolution on the 26th of December 1991. The state was formed by merging the Russian SFSR and its subordinate republics in 1922 and officially ended when Mikhail Gorbachev recognized its dissolution in 1991.
The Communist Party of the Soviet Union governed the state, with the General Secretary serving as the de facto highest office. Leaders included Vladimir Lenin, Joseph Stalin, Nikita Khrushchev, and Mikhail Gorbachev, who all held power within the Politburo or Central Committee structures.
Moscow served as the capital and largest city of the Soviet Union. The most populous cities throughout the state's existence were Moscow and Leningrad, followed by Kiev, Kharkov, and Baku, with Tashkent rising to fourth place by the end of the century.
At its height, the Soviet Union spanned eleven time zones and shared borders with twelve countries. It was the largest country by area and the third-most populous nation on Earth during its existence from 1922 to 1991.
The Soviet Union collapsed due to nationalist movements, economic stagnation, and an attempted coup by hardline communists that occurred from the 19th to the 21st of August 1991. This coup prompted Ukraine, Russia, and Belarus to secede, leading to the official dissolution on the 26th of December 1991.