In 1860 Tolstoy began work on a novel, The Decembrists, about a man who had taken part in the 1825 Decembrist Uprising. As he worked on the opening chapters, he came to realise that the roots of the Decembrist Uprising reached back to the events of the Napoleonic Wars, and stopped work on The Decembrists in order to start researching the novel that became War and Peace.
These scenes at the end of War and Peace are the last hints of the novel's original purpose. Tolstoy intended to write a sequel in which Nikolai Bolkonsky and Pierre Bezhukov would be involved in the uprising and exiled to Siberia. Marya's fears are foreshadowing the events of the sequel that was never actually written.
The Decembrist Uprising took place during the brief period of chaos after Tsar Alexander I's death. Although the Tsarevich Constantine had already renounced his claim to the throne, after Alexander's sudden death he was proclaimed emperor, only for this to be swiftly revoked as Nicholas I took control. While this was happening a group of liberal aristocrats called the Union of Salvation, who were dissatisfied with the repressive policies of the latter years of Alexander's reign, took the opportunity to rebel, hoping to force the government to seek a more liberal path. The society marched to Senate Square in St Petersburg, demanded reforms, but they failed to capitalise on their early momentum and were crushed by Nicholas's troops. The reactionary new tsar executed the rebellion's leaders and sent many others into exile in Siberia, where their suffering helped romanticise their cause, especially as many of the men's wives voluntarily followed them into exile. (Tolstoy planned for Natasha to become one such wife.) Their revolt is now considered the first expression of the revolutionary movement in Russia.
There is a modern American indie folk band called The Decemberists, named after this uprising. Listen to them on Spotify.