Lenin signed the Treaty of Brest-Litovsk, with Germany and had to give up Eastern Poland, Ukraine, Finland, and the Baltic provinces. Lenin promised the people and end to the war, redistribution of land, and to give the Soviets control of industry and government.
His promises to the people did not go through, and Russia sank into a civil war. The Allies and anti-communists, and tried to send troops to Russia to bring them back into war. Russia ended up converting to a full Communist nation, and the Allies decided to help their enimies.