Lenin returned to Russia from Switzerland on April 1917. He was helped by the Germans who expected him to seize power and make peace.
Lenin greeted the crowds at the Finland Station in Petrograd, where he gave a rousing speech. The gist of his words were later written down in the so-called April Theses, after Trotsky had also returned to Russia from the USA. They were published in the Petrograd party's official newspaper, Pravda
The April Theses demanded that power should be transferred to the soviets ,the war should be brought to an immediate end and all land should be taken over by the State and re-allocated to peasants by local soviets.
These demands have often been summed up as a demand for 'Peace, bread and land: Lenin also stressed a policy of non-cooperation with the Provisional Government, giving rise to a further motto: 'All power to the soviets'
Adapting Marxist theory, Lenin argued that the Russian middle class was too weak to carry through a full bourgeois revolution' and that to allow the middle classes to continue in power was to hold the inevitable proletarian revolution back.
The initial reaction to Lenin's reappearance was mixed
Some Bolsheviks feared that Lenin had grown out of touch and that his radical proposals would do more harm than good. There were allegations that Lenin was in the pay of the Germans (to some extent true).
The Mensheviks feared Lenin would undermine what they had been doing.
However, Lenin gradually built support with his speeches. By the end of April, Lenin won over the majority of the Central Committee of the Bolshevik Party by sheer force of personality.
Trotsky finally decided to join the Bolsheviks at the beginning of July.
Kerensky's determination to continue with the war played into the hands of the Bolsheviks.
However, the July days led to the warrants for the arrest of Bolsheviks, who were blamed for stirring up the troubles, were issued and several, including Trotsky, were jailed.
It is unclear whether the rebellion was actually stirred up by Bolsheviks and Lenin, always claimed that the demonstrations were spontaneous.
He immediately returned, but quickly fled in disugise into exile in Finland. Troops loyal to the Soviet dispersed the crowds and the Soviet newspaper Izvestia denounced the role of the Bolsheviks, suggesting that Lenin was working in the pay of the Germans and against Russias best interests.
Bolshevik propaganda was burned and the offices of the Bolshevik newspaper Pravda closed. Lenin's reputation fell.
On 8 July, Kerensky replaced Prince Lvov as Prime Minister and it might have appeared that the Bolsheviks' moment had passed.
But their cause was saved by the Kornilov coup. Bolsheviks were released from jail and soldiers workers again took to the streets, this time supposedly in defence of the Provisional Government. Kerensky even supplied them with arms.
Bolsheviks seized the opportunity to organise bands of workers commanded by their Red Guards, a militia they had trained in secret. The Bolsheviks were able to bask in the reputation of having been the only group to have opposed Kornilov consistently.
Lenin sent orders from Finland urging his followers to keep up the pressure and Committees to save the Revolution' were set up throughout the country. Consequently, Bolsheviks were elected in increased numbers to soviets in the Duma elections in Moscow.
Bolshevik support increased by 164% between June and December.
The Bolshevik membership, which had stood at 23,000 in February, had reached 200,000 by the beginning of October, by which time the party was producing mass newspapers and maintaining a force of 10,000 Red Guards in the capital's factories.
By September, when new elections were held to the Petrograd Soviet, the Bolsheviks won a majority, which together with their control of the Moscow Soviet placed them in a powerful position. On 21 September Trotsky became Chairman of the Petrograd Soviet.
The Bolsheviks were not, at this time, a tightly organised or disclined group. They tended to go along with events rather than initiate change
Lenin from Finland hinted of seizing power via revolution,but the Central Committee in particular its two most prominent members, Grigorii Zinoviev and Lev Kamenev, fearing that Russia was not yet economically ready for revolution, urged restraint and even burned some of Lenin's letters.