The Fifth Congress of the R.S.D.L.P. was held in London on April 30-May 19 (May 13-June 1), 1907. It was attended by 336 delegates, of whom 105 were Bolsheviks, 97 Mensheviks, 57 Bundists, 44 Polish Social-Democrats, 29 Lettish Social-Democrats and 4 non-factionalists. The Poles and Letts supported the Bolsheviks, who had a solid majority at the Congress. One of the main questions discussed was that of the attitude to the bourgeois parties. Lenin delivered the report on this question. On all fundamental issues the Congress adopted Bolshevik resolutions. A Central Committee was elected consisting of 5 Bolsheviks, 4 Mensheviks, 2 Polish and 1 Lettish Social-Democrats. Among the alternate members elected to the C.C. were 10 Bolsheviks, 7 Mensheviks, 3 Polish and 2 Lettish Social-Democrats.
The Fifth Congress of the R.S.D.L.P. marked the victory of Bolshevism in the Russian working-class movement. The decisions of the Congress summed up the struggle of the Bolsheviks against the opportunist, Menshevik wing of the Party in the period of the bourgeois-democratic revolution. The Bolsheviks' tactics were approved by the Congress and accepted as the tactics of the whole Party.
Golos Sotsial-Demokrata (Voice of a Social-Democrat ) -- a newspaper, the organ of the Mensheviks, published from February 1908 to December 1911, first in Geneva, then in Paris. The newspaper coming out in open support of the liquidators, Plekhanov resigned from the editorial board in May 1909, after which the paper took definite shape as the ideological centre of the liquidators.
Lenin is referring to the group of empirio-critics and empirio-monists, adherents of the reactionary idealist philosophy of Mach and Avenarius, namely, Bogdanov, Bazarov and Lunacharsky.