Saint Petersburg, formerly known as Petrograd and later Leningrad, is the second-largest city in Russia after Moscow. It is situated on the River Neva, at the head of the Gulf of Finland on the Baltic Sea. The city had a population of roughly 5.6 million residents as of 2021, with more than 6.4 million people living in the metropolitan area. Saint Petersburg is the fourth-most populous city in Europe, the most populous city on the Baltic Sea, and the world's northernmost city of more than 1 million residents. As Russia's Imperial capital, and a historically strategic port, it is governed as a federal city.

The October Revolution, also known as the Great October Socialist Revolution, October coup, or Bolshevik coup was a revolution in Russia led by the Bolshevik Party of Vladimir Lenin that was a key moment in the larger Russian Revolution of 1917–1923. It was the second revolutionary change of government in Russia in 1917. It took place through an armed insurrection in Petrograd on 7 November 1917 [O.S. 25 October]. It was the precipitating event of the Russian Civil War.