The Bund formally rejoined the RSDLP when all of its faction reunited at the Fourth (Unification) Congress in Stockholm in April 1906, with the support of the Mensheviks, but the RSDLP remained fractured along ideological and ethnic lines. The Bund generally sided with the party's Menshevik faction led by Julius Martov and against the Bolshevik faction led by Vladimir Lenin during the factional struggles in the run-up to the Russian Revolution of 1917.