There were several reasons for the revolution in 1917. One of them was Russia's defeat in the Russian-Japan war in 1905, which considerably damaged the reputation of the Russian government. Poor living conditions of working classes, and government's refusal to satisfy people's requirements for better life resulted in a demonstration of protest on January 9th, 1905, which was ruthlessly shot by the governmental forces; more than a thousand people died that day. Today this event is known as "the Bloody Sunday". This execution gave impulse to the revolution of 1905. It was suppressed shortly after, some basic civil rights were promised, the first Russian parliament (Duma) was elected, but it was obvious that the situation was about to explode.
The final drop was Russia's taking part in the World War I. By 1916 the country had lost more than 3,000,000 men, and people had no desire to fight and die for the Tsar any more. The Bolsheviks (Russian communists) used this unstable situation and captured the wills of millions of Russian with promises to finish the war, to give land to peasants and to build a state of equality.
In February 1917 the entire world observed the end of monarchy in Russia: strikes broke out in St.Petersburg, people took the streets and finally the tsar had to abdicate the throne. Now the power was in the hands of Workers' and Soldiers' Soviets. Later the Provisional Government was elected but it was still unable to solve the main problems. Under these circumstances the Bolsheviks decided that their time had come and started an armed uprising. In the night, October 26th, the Bolsheviks took the Winter Palace in St.Petersburg, former residence of the tsar occupied by the Provisional Government. A new era began.
Bolsheviks kept their promise and took Russia out of World War I. But exhausted and depressed people were about to face a new disaster - the Civil War. Moscow was made capital again, and from here Lenin and his government directed the "Red army" against anti-revolutionary coalition known as the "Whites". By November 1920 the Whites were thrown out of the country; the living symbol of tsar's Russia, Nikolay II and his family, was brutally butchered in Yekaterinburg already in 1918.