These reasons are the geographical location of the Red Army, Military strength and, my main point, the disunity of the opponents. In terms of geographical location, the Reds had dominated the main area of Russia which was the area between Petrograd, Moscow and Tsaritsyn which had a population of approximately 60 million. Moscow and Tsaritsyn were important in terms of industry as they contained a lot of factories, this area also included most of Russia's railway network so, this would help the Reds as they could use the railway network to send out munitions to soldiers or use the trains to disperse soldiers where and when they were needed.
Having the main area of Russia allowed the Red Army to conquer in the Civil War as they could produce more munitions then the White Army who has to rely on foreign support and, the Red Army could communicate more efficiently as their territory was continuous which allowed them to coordinate attacks against their enemies, unlike the Whites who were spread over large areas.
This information has been taken from Derrick Murphy in his book 'Russia in Revolution' and is also discussed in Mark Goslings book 'Russia in Revolution'. Both of these men are historians who are writing these books to inform and teach their audience, therefore in terms of provenance they are reliable as they can't be one sided. My second point as to why the Red Army conquered in the Civil War is the military strength of the Red Army and the military weakness of the opponents. Trotsky was a key person in the military for the Red Army. He made sure that offices who had fought for the Tsar were a part of the Red Army which provided the Reds with more experienced leaders. To ensure their loyalty to the Red Army, Trotsky held hostage families of those who were conscripted to the Red Army and those who had originally fought in the Tsarist army. In