The Mensheviks ('Minoritarians') and Bolsheviks ('Majoritarians') were two rival factions within the Russian Social Democratic Labour Party (RSDLP), also known as the Russian Social Democratic Workers' Party (RSDWP). The split occurred in 1903 and continued until the 1920s. The more moderate and cautious Mensheviks were led by Julius Martov (1873 to 1923), while the more revolutionary and pragmatic Bolsheviks were led by Vladimir Lenin (1870 to 1924). Fundamentally, the two factions had different ideas on how and when to stage a workers' revolution, which would achieve a socialist state that replaced the authoritarian rule of the tsar.

The Mensheviks' preference for a two-stage revolution, first by the bourgeoisie and then the workers, was perhaps more in tune with the ideas of the German philosopher Karl Marx (1818 to 83), who seemed to suggest in his work that a socialist revolution could only successfully occur in an industrialised and capitalist state, something Russia was not. The Bolsheviks, who wanted an immediate workers' revolution by any means, would also claim they were adhering to Marx's ideas since the philosopher had questioned whether a two-stage revolution was practically possible. Ultimately, a worker's revolution of sorts did take place through several months of 1917, although the revolutionaries were greatly assisted (to their surprise) by the disloyalty of the army to Tsar Nicholas II (reign 1894 to 1917), which caused his abdication. As more strikes occurred through 1917 and a provisional government was toppled, Lenin was able to form a new government of a new state: Soviet Russia. Lenin then had to win the Russian Civil War to secure his and the Bolsheviks' (now called Communists) position of power. Meanwhile, the remaining Mensheviks were either sidelined from the new Communist Party or left to live in exile.

The Russian Social Democratic Labour Party (RSDLP) was founded in 1898, but it was not a political party in the modern sense, but rather an underground revolutionary group. Tsarist Russia did not permit political parties. The RSDLP and other similar underground 'parties' strove to bring the downfall of the authoritarian Tsarist regime and its current head, Tsar Nicholas II. There was much rivalry and disagreement between and within these 'parties' as to what exactly should be the new system of government, as well as how and when such a change should be brought about.

At the RSDLP's second party congress in August 1903 (held in Brussels and London since most of the delegates were in exile from Russia), Vladimir Lenin's proposal for a revolution organised by "a few professionals as highly trained and experienced as the imperial security police" (Montefiore, 527) was not widely endorsed. Lenin consequently formed his own breakaway group, and since they had been the majority in certain congress votes (but only because many other delegates withdrew from the voting), they called themselves the Bolsheviks (from the Russian for 'majority': bolshinstvo). Lenin described his chief opponents as the Mensheviks, meaning the minority (Russian: mensheviki). Both of these terms are misleading if taken literally, since the number of adherents to each faction fluctuated over the years, and there were several other factions besides. For example, in 1910, the number of Bolsheviks within the RSDLP was estimated at only 10% by the key Bolshevik Leon Trotsky (1879 to 1940). On top of that, there were plenty of other revolutionary groups and parties besides the RSDLP, notably the Party of Socialist Revolutionaries, which had its own factions, including a sizeable group of revolutionaries who thought any sort of political party was a waste of time when faced with the ruthlessness of the tsar.

The Menshevik-Bolshevik rivalry and the fractured nature of the revolutionary Left would hamper ambitions to topple the establishment in Russia for the next two decades. In the shorter term, the lack of unity in socialist circles meant that they were unprepared for and unable to fully exploit the spontaneous Russian Revolution of 1905, a nationwide uprising that the tsar ultimately quashed.

The two factions of Bolsheviks and Mensheviks continued to work for the same revolutionary cause –establishing a fairer socialist society where peasants and workers were not exploited by capitalists and aristocrats – but it was a volatile relationship. The Bolsheviks wanted an elitist, closed, centralised, and secret-like inner core for the party leadership (to protect it from the tsar's secret police), while the Mensheviks wanted a more open leadership and a more inclusive party in general. The Bolshevik-Menshevik split was seen in socialist organisations across the empire from Georgia to Manchuria.

Another significant difference between the two factions was just how to achieve lasting change in Russian society. The Mensheviks, unlike some other groups, did not believe a wholesale revolution and establishment of a Marxist state were realistic possibilities, considering Russian conditions. Rather, the Mensheviks, who regarded themselves as Orthodox or Legal (because they worked within the existing laws) Marxists, considered it necessary to first have a 'bourgeois' revolution, which would overthrow the tsar and his capitalist allies. Only in a later, second phase, could there be a workers' or 'proletarian' revolution. Between these two revolutions, the Mensheviks called for workers to abstain from taking power themselves and instead present a permanent opposition through such bodies as workers' councils (soviets), trade unions, cooperatives, and local government councils. This 'revolutionary opposition' would effectively oblige the bourgeois institutions of state to promote some sort of minimum socialist programme. In addition, this two-step strategy would, in the meantime, the Mensheviks believed, allow Russia to develop its industry and increase political liberty to such a state that the workers could finally take over and achieve full socialism. Mensheviks believed that jumping straight to their 'second revolution' was far too risky and would endanger the whole process of achieving a fairer society for all.

The Mensheviks were here following the ideas of Karl Marx, or so they thought, since some critics would argue they were oversimplifying his ideas. Marx had suggested that a certain level of economic development and a certain range of political liberty were necessary for a state to be then successfully converted into a socialist society. This was because only a modern capitalist society would possess a sufficient number of politically enlightened workers to fuel the revolution. The Mensheviks were also following the ideas presented by Georgi Plekhanov (1856 to 1918), namely that the 'bourgeois revolution' was essential since at that stage of Russia's economic and political development (Russia was still semi-feudal in many respects), a full workers' revolution or 'maximalist' approach as it has been called, would be premature and lead only to an alternative form of despotism little different from the Tsarist regime. As things turned out in post-revolution Russia, the Mensheviks may have been right.

There were also factions within the Menshevik group. Disagreements were particularly evident during the First World War (1914 to 18). Some Mensheviks wanted a merely 'defensist' war to defeat German-Austrian militarism, while others supported a more 'internationalist' approach to the conflict (effectively not supporting either side). Some Mensheviks wanted to continue what was considered a patriotic war – a position known as 'revolutionary defensism' since victory would protect the achievements of the revolution. Lenin and his supporters, on the other hand, wished to end Russia's participation in the war immediately by whatever means possible. Another point of debate was the encouragement or discouragement of socialists outside Russia in the coming revolution. Finally, there were also Mensheviks who switched to becoming Bolsheviks (and back again), Plekhanov being a notable example.

The rival Bolsheviks had no patience for a two-stage revolution and called for an immediate and wholesale socialist revolution where the workers' soviets held power from the beginning. In this idea, they could also call upon Marx's work since the philosopher had suggested that, in reality, it would be difficult to separate the two revolutions the Mensheviks proposed. Trotsky, in many ways Lenin's deputy, was a key figure who endorsed this idea with his view that, practically speaking, there could not be a first and then a second revolution. Much more likely was a sort of rolling or 'permanent revolution'. There was also the point that the bourgeoisie might be too weak, too timid, and too self-interested to fulfil their part of the process, and so there would be no second workers' revolution because the first revolution had never even started.

Despite the ideological differences, there were, to add another layer to the complexity of loyalties, some Bolsheviks who thought it best to work with the Mensheviks regardless of the differing views. Other Bolsheviks wished to proceed with whatever was required to get the job done, with or without allies. Even Lenin himself often found his views in the minority within his own Bolshevik faction.

Lenin's practical policies were certainly quite different from those of the Mensheviks. Ever pragmatic, he employed a wide range of methods to agitate for revolution, some of which the Mensheviks (and even some Bolsheviks) did not approve of. Lenin did not, for example, want workers to vote in state elections; he advocated the use of paramilitary tactics, and he (secretly) endorsed the robbing of state banks and post offices to fund Bolshevik activities. Lenin also ensured the Bolsheviks were more modern than their rivals. For example, Lenin, besides converting the socialist newspaper Pravda ('Truth') in 1918 to become the rival to the Menshevik-dominated Iskra ('Spark'), also supported a newspaper that promoted the participation of women in the revolutionary cause. Minority groups were also encouraged to join the Bolsheviks. These policies did bear fruit, and the Bolshevik faction gradually grew in size within the wider socialist movement.

With their promises of more immediate change, the Bolsheviks were much more successful than the Mensheviks in gaining support from workers, who were becoming increasingly impatient with the tsar's vague and ultimately unrealised promises of reform. Factory workers in towns and cities were becoming increasingly radicalized, too, in no small part due to the Tsarist regime's harsh policies, such as controlling trade unions and refusing to listen to calls for reduced working hours and greater safety in working conditions. Workers formed their own factory committees, and these were increasingly infiltrated by the proactive Bolsheviks. Consequently, "these organizations enabled Bolsheviks to offer an alternative to the trade unions and to outflank their Menshevik rivals" (Freeze, 284).

Peasants in the countryside were just as impatient as the metal and textile workers in the cities to see revolutionary change. The Menshevik policy of trying to curb peasant violence worked against the faction, and they singularly failed to see that the radicalisation of Russian society meant there could never be much cooperation between the workers and bourgeoisie, two groups which seemed to be drifting ever-further apart. Most serious of all, the Menshevik attitude that authority should not be centralised in the RSDLP meant they limited their own participation in the party's decision-making and so diminished the possibility of controlling the Bolsheviks. In short, the Mensheviks had become a rather incoherent wing of the party since they had evolved "more as a broad tendency than as a political party" (Shukman, 67).

The Mensheviks did have strong support from the printers' union, the communication workers' union, and the chemical workers in Moscow. The Mensheviks also played a leading role in the soviets of the larger towns, in particular, the capital, St. Petersburg. The Bolsheviks, though, were much more dominant within the RSDLP itself. As the historian H. Shukman notes, "the Mensheviks never succeeded in capturing the party institutions" (80). Consequently, the Bolsheviks were able to declare that they were the true representatives of the RSDLP in January 1912. Lenin had persistently presented the Bolsheviks as "'hard, dedicated to ideological orthodoxy and organizational homogeneity, while the Mensheviks were vilified as 'soft', vacillating, liable to let sentiment and feelings cloud their judgement" (Shukman, 66). The Bolsheviks also had the upper hand when it came to public speaking. Lenin deliberately instructed orators at public meetings not to waste time on complicated arguments, which the audience had no hope of following, but stick to simple slogans like "Land to the working people!" and "Nationalization of plants and factories!" (Beevor, 93). The Bolsheviks eventually gained the upper hand in the various worker organisations.

The Russian Revolution of 1917 against Tsar Nicholas (actually two revolutions, one in March and a second, Bolshevik Revolution, in November) began with bread riots in Petrograd (the new name of St. Petersburg after 1914) in March 1917 and quickly escalated when troops of the Petrograd garrison joined the rioters. The revolution and the lack of support for the tsar amongst the political elite and army obliged Nicholas II to abdicate. There then followed a summer of unrest: 1917 "witnessed 1,019 strikes involving 2,441,850 workers and employees" (Freeze, 284).

The Mensheviks supported the new Provisional Government in their belief that this was the very 'bourgeoisie revolution' they had long hoped for. Meanwhile, the Bolsheviks, having now gained majority control of the Petrograd and Moscow soviets, seized the initiative. The Bolshevik calls for an immediate revolution and promises of 'Bread, Peace, and Land' had much more appeal to workers and peasants alike than vague promises of a revolution sometime in the future (several years in the future, according to the Mensheviks). As the revolution became increasingly violent, the Mensheviks protested over bombardment of the tsar's Winter Palace and warned that civil war now seemed inevitable. As the Mensheviks walked out of a meeting at the Petrograd Soviet in protest, Trotsky, speaking from the platform, taunted them with a now-famous line: "You are miserable bankrupts; your role is played out. Go where you ought to be: into the dustbin of history" (Suny, 135).

In November 1917, Lenin formed a temporary Workers' and Peasants' Government. In January 1918, there were elections for a new Constituent Assembly, but as the Bolsheviks won only one-quarter of the vote, Lenin dissolved it in a matter of days. Lenin effectively seized power but had to fight the damaging Russian Civil War between the socialist revolutionaries on one side and the various reactionary groups (including foreign powers) who wished to reinstate the tsar on the other. It was a conflict that the Bolsheviks eventually won. Although the Mensheviks sided with the Bolsheviks in the civil war – a choice of the lesser of two evils perhaps – they had no success in diminishing the Bolshevik revolutionary zeal and found themselves effectively driven into exile by 1921. Lenin had renamed the RSDLP party the Communist Party in March 1918, and he was finally able to establish Soviet Russia according to Bolshevik ideas. Lenin's critics, amongst them the Mensheviks, who continued to criticise while in exile, pointed out that, in the end, the revolution achieved little beyond ensuring Russia was once again ruled by a single authoritarian figure.