After the abdication of Tsar Nicholas II of Russia, the Russian Provisional Government was established during the February Revolution of 1917.
Formation of the Red Army
From mid-1917 onwards, the Russian Army, the successor-organisation of the old Russian Imperial Army, started to disintegrate; the Bolsheviks used the volunteer-based Red Guards as their main military force, augmented by an armed military component of the Cheka (the Bolshevik state-security apparatus). In January 1918, after significant Bolshevik reverses in combat, the future People's Commissar for Military and Naval Affairs Leon Trotsky headed the reorganization of the Red Guards into a Workers' and Peasants' Red Army in order to create a more effective fighting force. The Bolsheviks appointed political commissars to each unit of the Red Army to maintain morale and to ensure loyalty.
In June 1918, when it had become apparent that a revolutionary army composed solely of workers would not suffice, Trotsky instituted mandatory
conscription of the rural peasantry into the Red Army. The Bolsheviks overcame opposition of rural Russians to Red-Army conscription units by taking hostages and shooting them when necessary in order to force compliance, exactly the same practices used by the White Army officers. The Red Army utilized former Tsarist officers as "military specialists" (voenspetsy); sometimes their families were taken hostage in order to ensure their loyalty. At the start of the civil war, former Tsarist officers comprised three-quarters of the Red Army officer-corps. By its end, 83% of all Red Army divisional and corps commanders were ex-Tsarist soldiers.
While resistance to the Red Guard began on the very day after the Bolshevik uprising, the Treaty of Brest-Litovsk and the instinct of one party rule became a catalyst for the formation of anti-Bolshevik groups both inside and outside Russia, pushing them into action against the new regime.
A loose confederation of anti-Bolshevik forces aligned against the Communist government, including landowners, republicans, conservatives, middle-class citizens, reactionaries, pro-monarchists, liberals, army generals, non-Bolshevik socialists who still had grievances and democratic reformists voluntarily united only in their opposition to Bolshevik rule. Their military forces, bolstered by forced conscriptions and terror as well as foreign influence, under the leadership of General Nikolai Yudenich, Admiral Alexander Kolchak and General Anton Denikin, became known as the White movement (sometimes referred to as the "White Army") and controlled significant parts of the former Russian Empire for most of the war.
A Ukrainian nationalist movement was active in Ukraine during the war. More significant was the emergence of an anarchist political and military movement known as the Revolutionary Insurrectionary Army of Ukraine or the Anarchist Black Army led by Nestor Makhno. The Black Army, which counted numerous Jews and Ukrainian peasants in its ranks, played a key part in halting Denikin's White Army offensive towards Moscow during 1919, later ejecting White forces from Crimea.
The remoteness of the Volga Region, the Ural Region, Siberia and the Far East was favorable for the anti-Bolshevik forces, and the Whites set up a number of organizations in the cities of these regions. Some of the military forces were set up on the basis of clandestine officers' organizations in the cities.
The Czechoslovak Legions had been part of the Russian army and numbered around 30,000 troops by October 1917. They had an agreement with the new Bolshevik government to be evacuated from the Eastern Front via the port of Vladivostok to France. The transport from the Eastern Front to Vladivostok slowed down in the chaos, and the troops became dispersed all along the Trans-Siberian Railway. Under pressure from the Central Powers, Trotsky ordered the disarming and arrest of the legionaries, which created tensions with the Bolsheviks.
The Western Allies armed and supported opponents of the Bolsheviks. They were worried about a possible Russo-German alliance, the prospect of the Bolsheviks making good on their threats to default on Imperial Russia's massive foreign loans, and the possibility that Communist revolutionary ideas would spread (a concern shared by many Central Powers). Hence, many of these countries expressed their support for the Whites, including the provision of troops and supplies. Winston Churchill declared that Bolshevism must be "strangled in its cradle". The British and French had supported Russia during World War I on a massive scale with war materials. After the treaty, it looked like much of that material would fall into the hands of the Germans. Under this pretext began the Allied intervention in the Russian Civil War with the United Kingdom and France sending troops into Russian ports. There were violent clashes with troops loyal to the Bolsheviks.
The German Empire created several short-lived satellite buffer states within its sphere of influence after the Treaty of Brest-Litovsk: the United Baltic Duchy, Duchy of Courland and Semigallia, Kingdom of Lithuania, Kingdom of Poland, the Belarusian People's Republic, and the Ukrainian State. Following the defeat of Germany in World War I in November 1918, these states were abolished.
Finland was the first republic that declared its independence from Russia in December 1917 and established itself in the ensuing Finnish Civil War from January–May 1918. The Second Polish Republic, Lithuania, Latvia and Estonia formed their own armies immediately after the abolition of the Brest-Litovsk Treaty and the start of the Soviet westward offensive in November 1918.