When divisions among Russian Marxists between ‘Bolsheviks’ and ‘Mensheviks’ first emerged at the second congress of the RSDLP in 1903, they remained confined to secondary differences over organisational questions. Only with the 1905 Revolution did real political differences emerge, as Lenin explained in his brilliant pamphlet of that year, Two Tactics of the Social-Democracy in the Democratic Revolution. More than anything else, war and revolution bring out political differences with crystal clarity.