The Russian Civil War lasted from 1917 to 1922. It began immediately after the collapse of the Russian provisional government and the Bolshevik takeover of Petrograd, rapidly intensifying after Lenin's dissolution of the Russian Constituent Assembly and the signing of the Treaty of Brest-Litovsk. The main hostilities took place between Communist forces known as the Red Army and loosely allied anti-Communist forces known as the White Army, and the worst fighting took place from 1918 to 1920. The Communists won after four years of savage fighting, and established the Soviet Union in 1922.
Following the abdication of Russian Tsar Nicholas II and the turbulent Russian Revolution throughout 1917, a socialist-leaning Provisional Government was established. In October another revolution occurred in which the Red Guard, armed groups of workers and deserting soldiers directed by the Bolshevik Party, seized control of St. Petersburg and began an immediate armed takeover of cities and villages throughout Russia. In January 1918, Lenin had the Constituent Assembly violently dissolved, proclaiming the Bolsheviks as the new government of Russia.

The Bolsheviks decided to immediately make peace with Germany and the Central Powers, as they had promised the Russian people prior to the Revolution. This decision has also been attributed by historians to Vladimir Lenin's sponsorship by the foreign office of Kaiser Wilhelm II's Germany, offered by the latter in hopes that with a revolution, Russia would withdraw from World War I.

A cease fire was immediately announced and peace talks began. As a condition for peace, the proposed treaty by the Central Powers conceded huge portions of the former Russian Empire to Imperial Germany and the Ottoman Empire, greatly upsetting nationalists and conservatives. Leon Trotsky, representing the Bolsheviks, refused at first to sign the treaty while continuing to observe a unilateral cease fire, following the policy of "No fighting, but no peace treaty".


source: http://en.wikipedia.org