I recently did a quick post on some of the key factors here. Happy to answer any further questions you may have.

There are several:

• The Reds controlled the most densely populated areas of the country, including most of the industry. The Whites were mostly relegated to the fringes of the country. The Reds had an advantage in conscripting new troops and in production of materiel.

• The Reds controlled most of the railways. This was huge. This allowed them to quickly shift and reinforce troops from one section of the front to another. This is what is called "interior lines". The Whites, by contrast, were geographically isolated from one another which made it difficult for them to coordinate or help each other.

• The Reds were more politically astute. They were better politicians, so to speak. They understood what the population wanted. They had better propaganda. They were less ideologically rigid which may come as a surprise. For instance, the Whites mainly adopted a stance of "united and undivided Russia" which alienated many ethnic minorities who wanted independence or autonomy. The Reds were able to appeal to those groups better (even if their appeal wasn't entirely genuine). In short, the Reds were better at winning the hearts and minds of the people.

• The Reds were also really good at using sticks. For instance, they arrested or took hostage family members of tsarists generals and instituted the commissar system. This ensured that the generals who might otherwise not be very loyal to them were under their control.