==Руски грађански рат==
''Main article: [[Russian Civil War]]''
A powerful group of counterrevolutionaries termed the [[White movement]] began to organize to topple the Bolsheviks. At the same time the Allied powers sent several expeditionary armies to Russia to support the anti-Communist forces. The Allies feared that the Bolsheviks were in a conspiracy with the Germans because of Brest-Litovsk; they also hoped that the White Russians might renew hostilities against Germany. In the fall of 1918 the Bolshevik regime was in a perilous position, opposed by Russia's former allies and internal enemies, as well as in sporadic conflict with short-lived nationalist republics in Belarus and Ukraine and anarchist forces.
To counteract this emergency, a reign of terror was begun within Russia as the [[Red Army]] and the [[Cheka]] (the secret police) destroyed all enemies of the revolution. However lofty their goals were, the Bolsheviks did not have the consent of all elements of society and thus had to force their rule over Russia during the civil war. They swept away the tsarist secret police, so despised by Russians of all political persuasions, along with other tsarist institutions, but ensured the survival of their own regime by replacing it with a political police of considerably greater dimensions, both in the scope of its authority and in the severity of its methods. By [] all White resistance had been crushed, foreign armies evacuated, and Bolshevik governments established in Belarus, Ukraine, and the Caucasus, but at the cost of perpetuating Russia's long pattern of autocratic rule in new forms.
As Russia was bogged down in civil war, the frontiers between Poland and Russia were not clearly defined by the postwar [[Treaty of Versailles]] and were further rendered chaotic by the civil war. The [[Polish-Soviet War]] (1919–1921), which ended with the defeat of the Red Army, determined the borders between Soviet Russia and Poland.