Why was there a civil war in Russiain 1918 to 1921?

As soon as he gained power, Lenin made clear what he intended to do. A "Land Decree" was issued which said that land now belonged to the people who farmed it. This was followed by the "Peace Decree", which stated that the war with Germany was over. These decrees were intended to win support for the Bolsheviks (the Reds), but Lenin's plans did not work. When a general election was held in November 1917, the Bolsheviks came second to the Socialists-Revolutionaries.

Lenin's response was simple. When the new Russian Parliament, the Constituent Assembly, met on 5th January 1918, it was dispersed and Lenin began to rule as a dictator. Other political parties were banned, newspapers were censored and a secret police force was set up, the Cheka, led by Felix Dzerzhinsky. They enforced Lenin's ideas and thousands of people were murdered. All businesses and banks were taken over, many landowners and landlords lost their land to the peasants. In March 1918 a peace treaty with Germany was signed at Brest-Litovsk. Russia left the First World War. All the loans, which the Allies had given to Russia, were repudiated. Lenin made many enemies and they all came together to try to overthrow the new Bolshevik government. Britain,France and the USA. Together these forces were known as the Whites. But the Reds, as the Bolsheviks were called, were better equipped and had more men. Many Russians did not want a return to rule by the Tsar. By 1920, the White armies had all been defeated and the Bolsheviks controlled Russia.