The sixth All-Russian Conference of the Russian Social Democratic Labour Party (Prague Party Conference) opens. In the course of the conference, Vladimir Lenin and his supporters break from the rest of the party to form the Bolshevik movement.

The Russian Social Democratic Labour Party (RSDLP), also known as the Russian Social Democratic Workers' Party (RSDWP) or the Russian Social Democratic Party (RSDP), was a socialist political party founded in 1898 in Minsk, Russian Empire. The party emerged from the merger of various Marxist groups operating under Tsarist repression, and was dedicated to the overthrow of the autocracy and the establishment of a socialist state based on the revolutionary leadership of the Russian proletariat.

The Prague Conference, officially the 6th All-Russian Conference of the Russian Social Democratic Labour Party, was held in Prague, Austria-Hungary, on 5–17 January 1912. Sixteen Bolsheviks and two Mensheviks attended, although Joseph Stalin and Yakov Sverdlov were unable to attend because they were in internal exile at the time, while Georgi Plekhanov claimed he was too ill to attend. At the conference, Vladimir Lenin and his supporters broke away from the rest of the Russian Social Democratic Labour Party and formed their own predominantly Bolshevik Russian Social Democratic Labour Party. The conference was meant to be secret; Lenin had instructed: "No-one, no organisation must know about this". However, every detail was known to the Okhrana, the secret police of the Russian Empire.

Vladimir Ilyich Ulyanov, better known as Vladimir Lenin, was a Russian revolutionary, politician and political theorist. He was the first head of government of Soviet Russia from 1917 until his death in 1924, and of the Soviet Union from 1922 until his death. As the founder and leader of the Bolsheviks, Lenin led the October Revolution which established the world's first socialist state. His government won the Russian Civil War and created a one-party state under the Communist Party. Ideologically a Marxist, his developments to the ideology are called Leninism.