Adrian Li and Hugo Chan, two keen Chinese students who are working on a project concerning communism in Russia asked us the above question.
Russia was backwards in many ways under the Tsar. Anno 1914 it had an outdated mentality. The church and the aristrocracy were oppressing the people and trying to keep them in line with the old traditions, but at the same time the country was developing. It was developing faster than most people realize, in terms of railroads, industry, etc, though it was still lagginf behind western nations.
Ever since 1814, when the russian army made it to France, some people in russia believed in the ideals of the French revolution. This led to the failed uprising of 1825, among other things. The main reasons communism spread so rapidly were: it was something new, lots of people always long for change, Lenin offered peace on any terms, and many people desperately wanted peace, the Germans had also given Lenin plenty of money to set up a propaganda machine. Plus the farmers were promised land. Serfdom had only been abolished in 1861. Only half a century before. The peasants thought they could get more freedom. Under the NEP, new economic policy, of Lenin, quite a few peasants did grow wealthy, but Stalin would crush them later.
A nucleus of well organized well funded communists managed to take over the country, because it was in chaos because of a dismal war effort. I think the ideas of peace and land for the peasants, plus the funding from Germany, plus the weak Tsars Russia had had for so long, were the crucial factors.
Ironically the communist revolution happened in a mostly agricultural society, Marx had expected it to happen in a highly industrialized nation such as Germany, but there the veterans of WWI bloodily beat back the communists. The old German order was stronger than the old Russian order. Russian peasants thought they had something to gain from what was happening in the cities, like in Petrograd, where the communists grew stronger. In Germany the old order somehow had more to offer than in Russia, and it swung to the right, it also developed into a totalitarian regime, but the rich class stayed the owners of the means of production, the work force was kept in line through a different philosophy than in the Soviet Union. Although the political philosophies of both nation were radically different, in practice they were eerily similar.
This is our answer in a tiny nutshell…