One reason why the soviet union grew slowly in the 20th century compared to the united states and western europe was that it:

The Communist Party of the Soviet Union followed Marxism-Leninism.  The party pursued state socialism which involved a nationalized and planned economy.  Without individual motivation, as was encouraged in the U.S., the people grew tired of working for the State.  The Soviet Union might have survived if  restructuring had taken place years before Gorbachev tried it and  their economy had become a market economy.  Instead it was allowed to grow stale and to stagnant which caused the collapse of the Soviet Union.