[This article is excerpted from volume 2, chapter 12 of An Austrian Perspective on the History of Economic Thought (1995). An MP3 audio file of this chapter, narrated by Jeff Riggenbach, is available for download.]
There is no place in his system where Marx is fuzzier or shakier than at its base: the concept of historical materialism, the key to the inevitable dialectic of history.
“The task of fighting Marxian dialectical materialism and all the various epistemological, philosophical, economic, and political doctrines emanating from it can only be accomplished by well-informed people. Those who want to contribute seriously to the defense of Western  civilization against the onslaught of the dictators must acquaint themselves with the doctrines they plan to fight and must with full vigor study the writings of those authors who have long since entirely demolished all the Marxian fables and distortions. One has to admit that this is not an easy matter. Yet, there are in this world no great things that can be accomplished but by moral resolution and strenuous exertion.” Mises