If your library is well-stocked with works devoted to the 1918-1953 era you might find the book's treatment of that era superficial. It does offer a readable summary of the era's events, without editorializing or stretches to cram the information into a "theoretical" (the way the humanities types abuse the word) framework. Start with this work, then ask me where to look for deeper insights. (Many of the answers to that question are visible on the shelves. Just enlarge the picture.)
The book suggests the Germans were closer to surrounding Moscow in October of 1941, and changing the subsequent war in the east, than I was aware. More surprising, though, was the effort the author, who holds an endowed chair at Florida State, made to apologize to colleagues for including Lenin in the Unholy Trinity. The myth of the Communist Revolution being started by the "good" Lenin (Polymorphous perversity! No-fault divorce! Priests at hard labor! Bankers and commodity speculators against the wall!) and betrayed by the "bad" Stalin (Socialist-realist painting and music(*)! Your neighbors at hard labor! Old comrades against the wall!) dies hard. What's that Orwell line about ideas so crazy only an academic would believe them? The Communist machinery of oppression began with Lenin. If you don't believe Professor Gellately, I have a wall of books you can browse.
(*)But for Stalin, Prokofiev and Shostakovich would be two more obscure writers of soporific and un-listenable tenure music is as a feather to a trainload of Powder River coal in weighing Stalin's record.
(Cross-posted to Cold Spring Shops.)