The cause of the war was that the provisional government, led by Alexander Kerensky, had failed. People were demanding for many things. Lenin and hid people had attacked the provisional government and had ended private ownership. The Bolsheviks were later called Communists.
Russia had signed a treaty where they would lose land, but they had received peace with the Central Powers. It had also ended Russia's involvement in WWI.
The "White" army wanted to defeat the Bolsheviks. Allies had joined and hoped the Whites would overthrow the Communists and help the Whites as well. The Reds tried to make the Russians drive out foreigners.