Meaning "majority" in Russian, the Bolshevik party was formed after the Second Congress of the Russian Social Democratic Labour Party in 1903.
The Congress as a whole had agreed on the tactics for the coming revolution: the need for a revolution in Russia was clear, and members agreed on the ultimate end: to establish Socialism.
The party adopted a theory of societal evolution; that with the yoke of feudalism thrown off, a capitalistic system should be built; i.e. society needed to naturally evolve along a set pattern of progression: from feudalism to capitalism to socialism to communism; one stage needed to be completed before the next was possible.
The Congress divided over several issues, one was over what kind of members would make up the party.
What would become the Menshevik portion of the party, among its leaders were Pavel Axelrod, who believed that membership to the party should be as broad-based as possible, appealing to the widest possible group of workers in order to have a stronger party through mass numbers.
What would become the Bolshevik portion of the party, with Lenin at its head, stressed the need for militant revolutionaries in the party, believing that with the extreme political persecution in Russia coupled with the revolutionary party programme, the party could not stay on course if workers who joined were not fully dedicated to a revolutionary programme.
Lenin stressed the need to differentiate between trade unions and revolutionary organisations in countries where political oppression was extreme to the extent that mixing the two together would drive both into persecution. By separating the illegal revolutionaries from the legal trade unions, Lenin explained, the trade unions can continue to operate legitimately while the revolutionaries, being a smaller organisation, can be more secretive to avoid detection and better trained to combat police.
On January 9, 1905 (Bloody Sunday) "the Russian proletariat burst on the political stage as a class for the first time", in a series of bloody strikes and protests that would become known as the Russian Revolutions of 1905.
The differences that had split both parties faded away, as both parties came together in the revolutionary events. During the revolutionary events the parties combined work accomplished great organisational and agitation feats among the working class, helping to sharpen their demands and gain greater freedoms for Russia's workers and peasantry.
With the revolutionary events ending, the parties went head to head again, abuzz over tactics on new approaches to the struggle based on these revolutionary events. Plekhanov's theory of the revolutionary base being solely invested in Russia's proletariat was shown to be incorrect, as the peasantry had led much of the revolutions of 1905. The Mensheviks, regardless, remained entrenched to the orthodox belief of the revolutionary role of the proletariat, while the Bolsheviks believed that while the proletariat would lead the Socialist revolution, it could only do so with the peasantry in its ranks.
The two parties conflicted more heavily over an examination of the true nature of the 1905 revolution. The Bolsheviks explained that the revolution had been bourgeois in nature, showing the rising strength of the industrial bourgeoisie and the increasingly capitalistic Russia. While the Tsar was still in power, numerous concessions left the government partly in the hands of the newly formed Duma, staffed by the bourgeoisie.
The Mensheviks, however, believed that capitalist government had obviously not been fully established (the autocracy still stood), and therefore it was still necessary for the working class to struggle towards overthrowing the tsar and establishing a bourgeois government.
By the beginning of the 1910s, with the fire of revolution in Russia cooled, support of Bolshevik principles became nearly non-existent. At the outbreak of the World War I, the Bolsheviks were one of the only political groups in Russia to agitate relentlessly for an end to the war, explaining that it was imperialist butchery driving the working classes into a war that divided and slaughtered them. Such agitation caused vicious police persecution of the party: Bolshevik leaders and members were ordered arrested. Lenin managed to escape persecution and travelled to Switzerland, the only country that would allow the Russian revolutionary within its borders. This dispersal of the party added to its political disintegration, though a core group remained.
By the time of the February Revolution, the Bolsheviks who had remained in Russia, to extents safe from Tsarist persecution, were pressing support of the Provisional Government, though, like the Mensheviks, with the eventual aim of struggling for its overthrow.
On April 4, 1917, Lenin arrived in Petrograd and delivered his April Thesis to the Social-Democratic parties: explaining a new Bolshevik programme, amidst the opposition of nearly the entire party. He explained that now was the time to establish a Socialist society; before the bourgeois provisional government became entrenched, but with decades of capitalist development to build on. Within a few weeks the entire Bolshevik party had moved to support Lenin's revolutionary programme.
By contrast the Mensheviks supported its members holding posts in the Provisional government. Initially, the government, led by the Cadet party, agreed to allow the Socialists in through a Contact Commission. The Bolsheviks ardently opposed this, for the commission had no real power whatever, and acted only as advisors.
Street protests and strikes forced the government to allow Socialists in the government in real positions, creating what was known as the Coalition Provisional Government. The Bolsheviks opposed its formation, seeing it as a charade. Despite Bolshevik objections, the majority of the Petrograd Soviet elected to go forward with the coalition, and the Bolsheviks sent one of its members, Kamenev, to help form the coalition. No Bolsheviks were allowed into the government.
On October 24-25, 1917, the Bolshevik party led the workers and peasants of Russia to overthrow the Provisional Government and establish the Soviet Government. The next day, upon the convocation of the Second Congress of Soviets, decrees were past on giving land back to the peasantry and forming a peace on all fronts.
While the majority of the workers and peasants had supported the Soviet government, the major political parties of Russia: Mensheviks and SRs (except the Left SRs, who joined the government), coupled with all parties further to the right, united in agitation against the Soviet government. This extreme political isolation, effectively limiting the Soviet government to be represented by only one political party and some independents, coupled with the coming four years of civil wars, changed Bolshevism completely.
After Lenin's death, the once fluid principles of revolutionary Bolshevism were made into concrete, no longer principles that changed as history progressed, but instead fixed ideas that would last for all time: the neo-Bolshevism was a coupling of Lenin's uncompromising passion with a select few of his ideas.
A struggle ensued between the right and left wing of the Bolshevik party, completely behind closed doors. Discussions that had once been made publicly, political attacks that had once been known by every reader of the party's newspaper Pravda, were now completely hidden from the public.
Trotsky, supporting the left wing, and Stalin, supporting the centre, went head to head in debates; both accusing each other of betraying the "principles of Lenin", which meant betraying Bolshevism, and as a result was twisted into meaning a betrayal of the Soviet Union.
In 1927, Stalin won the debate, and purged the Left Opposition, not only from the party, but from their positions in the Soviet government. Trotsky was not only purged from the party and government, but his Soviet citizenship was revoked.
The party, what remained of it - more than two-thirds of the Bolsheviks that had participated in the October Revolution were no longer in the party - then moved to take command over the Soviet government: being the only political party whose opinion was "valid", it followed that the party, not the Soviets, was in ultimate control over the government, and thus, all people in the Soviet Union....
Encyclopaedia of Marxism