Party Unity, German Aid, the Whites were falling apart, and they were very organized. The idea of Communism/Socialism was very intriguing and people were interested in it, and his party promised prosperity and a lot of things, which sounded very attractive to people.
WW1 is a big event that brought him to power, to avoid a war with Russia, the Germans sent Lenin and allies with LOTS of money and LOTS of resources.
