E. H. Carr, "Karl Marx: His Life and the Formation of His Thought" - Recommended biography with excellent analysis of "Why Marxism Attracted People".
The greatest appeal of this biography is, above all, the analysis of why Marx attracted so many people.
There is tremendous value in this book just to read this analysis. In fact, I might even say that you should pick up the book to read this analysis. It is such a sharp analysis. I highly recommend this book!