Instead...they succeeded in their stated goals, bringing happiness and prosperity to all?
At least in the case of Stalinist Russia, happiness wasn't the goal. The incredibly rapid industrialization of Russia was and that was a tremendous success though at a horrible human cost. It's no secret that non-democratic states are much more efficient than democratic ones.
The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth. -- Niels Bohr