Kazan Operation was the Red Army's offensive (510 September 1918) against the Czechoslovak Legion and the People Army of Komuch during the Russian Civil War.

The Russian Civil War (Russian: Гражданская война в России, tr. Grazhdanskaya voyna v Rossii; 7 November 1917 — 16 June 1923) was a multi-party civil war in the former Russian Empire sparked by the overthrowing of the monarchy and the new republican government's failure to maintain stability, as many factions vied to determine Russia's political future, resulting in the formation of the RSFSR and later the Soviet Union in most of its territory. Its finale marked the end of the Russian Revolution, which was one of the key events of the 20th century.

The Russian monarchy had been overthrown by the 1917 February Revolution, and Russia was in a state of political flux. A tense summer culminated in the Bolshevik-led October Revolution, overthrowing the Provisional Government of the Russian Republic. Bolshevik rule was not universally accepted, and the country descended into civil war. The two largest combatants were the Red Army, fighting for the Bolshevik form of socialism led by Vladimir Lenin, and the loosely allied forces known as the White Army, which included diverse interests favouring political monarchism, capitalism and social democracy, each with democratic and anti-democratic variants. In addition, rival militant socialists, notably Makhnovia anarchists and Left SRs, as well as non-ideological Green armies, opposed the Reds, the Whites and foreign interventionists. Thirteen foreign nations intervened against the Red Army, notably the former Allied military forces from the World War with the goal of re-establishing the Eastern Front. Three foreign nations of the Central Powers also intervened, rivaling the Allied intervention with the main goal of retaining the territory they had received in the Treaty of Brest-Litovsk.

The Bolsheviks initially consolidated control over most of the country. They made an emergency peace with the German Empire, who had captured vast swathes of Russia in the chaos of the revolution and the context of World War I. In May 1918, the Czechoslovak Legion in Russia revolted in Siberia. In reaction, the Allies began an intervention in Northern Russia and Siberia. That, combined with the creation of the Provisional All-Russian Government, saw the reduction of the Bolsheviks to most of European Russia and parts of Central Asia. In November, Alexander Kolchak launched a coup to take control of the Russian State, establishing a de facto military dictatorship.

The White Army launched several attacks from the east in March, the south in July, and west in October 1919. The advances were later checked by the Eastern Front counteroffensive, the Southern Front counteroffensive, and the defeat of the Northwestern Army. The White Movement also suffered greater loss as the Allies pulled back from northern and southern Russia. With the main base of the Russian SFSR secured, the Soviets could now strike back.

The armies under Kolchak were eventually forced on a mass retreat eastward. Soviet forces advanced east, despite encountering resistance in Chita, Yakut and Mongolia. Soon the Red Army split the Don and Volunteer armies, forcing evacuations in Novorossiysk in March and the Crimea in November 1920. After that, anti-Bolshevik resistance was sporadic for several years until the collapse of the White Army in Yakutia in June 1923, but continued on in central Asia and Khabarovsk Krai until 1934. There were an estimated 7 to 12 million casualties during the war, mostly civilians.: 287 Many pro-independence movements emerged after the break-up of the Russian Empire and fought in the war.: 7  Several parts of the former Russian Empire—Finland, Estonia, Latvia, Lithuania, and Poland—were established as sovereign states, with their own civil wars and wars of independence. The rest of the former Russian Empire was consolidated into the Soviet Union shortly afterwards.