What is Communism vs. Fascism?

We all know that Marxist Socialism was never established in Russia. Stalin's Communist Party was nothing more than a name. It never followed true communist ideals. No instead of a dictatorship of the proletariat, a dictatorship of Stalin was established. I still lack some basic fundamental understanding of fascism, but I find it difficult to tell the difference between Stalin's Russia and Fascist Europe. Hitler and Mussolini were dictators. Stalin was one too. There does not seem to be much difference in the way they did things. So why did they hate each other? That is one thing I will never really understand. The book says that Communists were left wing, but I do not understand how there can be anything liberal about rule under a dictator.

It must only be in the name. I guess this should not be too surprising that this would be enough for Hitler to not like Stalin, given Hitler's racist beliefs. It might have also stemmed from his belief that Slavs were inferior people. Whatever the reason, the resulting alliance between Russia and the West after Hitler's attack on Russia seems very unlikely. Of course that was the cause of the post-war tensions and the split between NATO and the Warsaw Pact. It is interesting to see that people of very different ideologies can unite against a common foe.