The Bolsheviks held the central position. The Whites were widely separated and did not coordinate their attacks very well. The Bolsheviks were able to crush Denikin at the battle of Orel in October 1919, before they had to worry about Admiral Kolchak and his attack from the east.
Source: "The Cultural Atlas of Russia and the Former Soviet Union" by R R Milner-Gulland and Nikalai Dijeuski. Specifically the map of the Russian Civil War of 1918-1920.

As Davratta said, White forces were dispersed and mostly in peripheral positions. Furthermore, neither the Whites nor the foreign intervention forces made up a coherent whole. There was many White forces, ideologically ranging from monarchist, nationalists in various degrees of extremism, etc. And for most part, White forces found little popular support due to many of them conducting a very brutal repression policy on either national or class basis. Similarly, British, French and American intervention took place at different points, Murmansk, Odessa, far East. That enabled the Bolsheviks to deal with individual forces in order.

Still, in the chaos after the war and Brest-Litovst treaty, with the extremely war weary population, and with their promises of peace and land, it was by no means certain that Bolsheviks would be able to motivate enough people to fight for long enough to win. Organizationally, Trotsky did a lot to make Red army a respectable and coherent fighting force. Ideology, boiled down to easily transmitted snippets (mentioned land and peace, liberty, equality, fruits of the labour for the workers, Soviet power, etc. etc.) proved capable of motivating enough people. Unlike social-democrats who supported their governments at the outset of First world war, consistent communist pacifism from the outset gave them additional credibility in claiming a just and unavoidable war. That, and utopian vision of a world to come out of that cataclysm, also made communism an attractive option, not just in Russia but also Germany (Bavarian Soviet Republic, uprisings led by Rosa Luxemburg and Karl Liebknecht), Hungary (revolution in 1919), north Italian revolutionary movements (factory councils, general strikes, red Turin), and among many demobilized or deserted soldiers in countries without clear revolutionary movements.