Update: This post is a good example of the power of the 'eonic model'. But it requires study and a reading of Decoding World History and/or The Last Revolution  (see the links on the sidebar) would help. But the left is so ingrained in the bad theories of Marx that it is virtually hopeless to communicate. The 'eonic model' so-called is not a theory but an outline of historical evolution. But it requires studying world history. The simple chronology in the model is very easy to understand, not so easy is the reading of historical books on world history. But the outline can be a start. For reasons that the 'eonic model' makes clear there is no way to a science of history, although the eonic effect as such points to such a theory which would be extremely complex. The academic world is unable to handle this kind of model because they are confused about Darwinian evolution. The evolution question is simply mishandled by biologists with their obsession with natural selection. The error is so simple that failure to grasp its implications makes us wonder about academics.  The material below can be taken simply as a warning that historical materialism is not scientific at all. Nothing in reaching socialism requires Marx's theories. And it is very doubtful if Marxists can help us to reach socialism, which predates Marx, and they are really one more obstacle on that issue.

Source: A Marxist Appraisal of Howard Zinn's "A People's History of the United States" - Socialist Revolution
Zinn's classic is rightly respected on the left but the book in detailing the crimes of American history has nothing to say about the crimes of the left, which, to be sure, is not the book's topic, and yet the impression given results in a kind of propaganda and gives the appearance of deception in a socialist.
And then again the analysis of the book at Socialism Revolution is typical Marxist mishmash and theory fallacy. To criticize a historian for being moralistic is Marxist idiocy and the whole issue of historical materialism creates a wrong-headed perspective and over and over again misunderstands history. Read more of this post