The Germans, being no fools, set to take advantage of the coup behind the lines of their Eastern Front and dispatched Lenin in a sealed train from exile in Switzerland to the turmoil in Russia, where he arrived in St. Petersburg to stoke the fire of revolt in 1917. In exchange, Lenin vowed to end the war, closing the Russian front; it was a deal similar to that Germans made with Irish rebels a year earlier.
The provisional government had set up a new Duma, which — much like the National Assembly in pre-revolutionary France — had been a puppet advisory council to the monarch, but this time as a real parliament. The Duma became a hornets’ nest of opinions, including socialists.
Parallel to the Duma, government power devolved to a network of grassroots community assemblies (called “soviets”). These were modeled after the workers councils that had been set up in the abortive revolution of 1905; John Reed offers the best description of how they functioned, which was by a fairly chaotic consensus. The net effect was that the Provisional Government and Duma made grand policy and legislation, but at the local level people obeyed the soviets, which also formed militias to defend against armed bands of Tsarists.
In October (November in modern calendars), the Bolsheviks, under a committee led by Lenin led an armed revolt of workers and soldiers, under the slogan “peace, bread and land.” They seized the capital, Petrograd (St. Petersburg), overthrew the government and transferred its authority to the soviets. The very first people Lenin ordered shot, on the first morning of the new regime, were 2,000 members of what was then called the Social Revolutionary Party, much more moderate than the Bolsheviki, despite the name.
Lenin halted the war, signed a peace treaty with Germany in March 1918, launched a campaign of “red terror” (similar to Robespierre in the French Revolution) operated by the Cheka (a secret police that was almost identical originally to the Tsar's Okhrana) to bring opponents (many of them socialists) to heel. A Civil war broke out, indeed Britain, France and the United States sent troops to help the “White” counter-revolutionaries against the “Red” Bolsheviks, which the latter won. Lenin's group named itself the Communist Party and formed, in 1922, the Union of Soviet Socialist Republics.