Without a doubt many thousands of books have been written about Adolf Hitler's rule in National Socialist Germany, and Joseph Stalin's less officially stated rule of Russia / the Soviet Union. Given the impact and the importance of these two twentieth century dictators these books have been written in many different languages. Relatively few of these numerous biographies and history books have directly compared these fascinating yet despicable dictators. Before I brought and read this book the best example I had come across was Alan Bullock's Hitler and Stalin Parallel Lives of 1991 (which I found very useful for undergraduate history essays).
Richard Overy published this excellent study of both Adolf Hitler and Joseph Stalin back in 2004. Overy had already written many military history books as well as books about both the Third Reich and the Soviet Union. Thus he had already acquired a great deal of knowledge about their respective dictatorships, and their titanic struggle against each other in the Second World War. Indeed the merciless conflict on the Eastern Front between 1941 and 1945 remains the bloodiest conflict in human history.
Overy's study is around three hundred pages shorter than Bullock's earlier masterpiece yet it still has 650 highly informative pages covering every aspect of the two dictators from their birth, their flawed childhoods, their struggle for power, and then their differing fortunes in the Second World War. You can tell this is thoroughly well researched as there are 180 odd pages for the bibliography and footnotes.
This is a masterly evaluation of what made Hitler and Stalin two of the most powerful men in history, and without doubt the men responsible for ordering and causing more violent death than any others before or since. Despite their evil actions and intentions both men were popular domestically as well as gaining admirers abroad.