It was not the first Russian Marxist group; the Group for the Liberation of Labour was formed in 1883. At the first party congress in 1898, all nine delegates were arrested. The RSDLP was created to oppose narodnichestvo (народничество), revolutionary populism, the program of the Social Democrats (SDs), who later joined the Socialist-Revolutionary Party (SRs; эсэры). The RSDLP program was based on the theories of Karl Marx and Friedrich Engels - that, despite Russia's agrarian nature, the true revolutionary potential lay with the industrial working class.
Before the Second Congress, a young intellectual called Vladimir Ilyich Ulyanov (Владимир Ильич Ульянов) joined the party, better known by his pseudonym - Lenin (Ленин). In 1902 he had published What is to be Done?, outlining his view of the party's task and methodology - to form 'the vanguard of the proletariat' needed a disciplined, centralised party of committed activists.
In 1903, the Second Congress of the party met in Belgium to attempt to create a united force. At the congress, the party split into two irreconcilable factions on November 17: the Bolsheviks (большевик; from Bolshinstvo - Russian for "majority"), headed by Lenin, and the Mensheviks (меньшевик; from Menshinstvo - Russian for "minority"), headed by Julius Martov. Confusingly, the Mensheviks were actually the larger faction among the party rank-and-file, but the majority of the party leadership sided with Lenin; hence, their faction took the name Bolshevik. It was Lenin's uncompromising stance on pushing his ideas, particularly on the issue of party membership, that caused the split. Lenin argued that creating a successful revolution required that party membership be limited only to professional full-time revolutionaries; whereas the Mensheviks favored an open membership policy. Despite a number of attempts at reunification, the split proved permanent.
The SDs boycotted elections to the First Duma (April-July 1906), but were represented in the Second Duma (February-June 1907). With the SRs, they held 83 seats. The Second Duma was dissolved on the pretext of the discovery of a SD conspiracy to subvert the army. Under new electoral laws, the SD presence in the Third Duma (1907-12) was reduced to 19. From the Fourth Duma (1912-17), the SDs were finally and fully split. The Mensheviks had five members in the Duma and the Bolsheviks had seven, including Roman Malinovski, who was later uncovered as an Okhrana agent.