Why the Allies Won is just right in every way: just the right level of detail; just the right level of analysis; just the right tone; just the right amount of acknowledgment of other points of view; just the right level of specifics versus general lessons. Regarding that last, consider this: “By December  the Panzer armies were using horses again. These were rates of loss never anticipated by German leaders. Little thought or preparation had gone into the question of what to do if the quick campaign of annihilation failed. The German army too needed to modernise in 1942.” Lesson: Always consider the worst-case scenario. What do you do if things go spectacularly wrong? It’s a lesson the Bush administration didn’t learn before invading Iraq. It’s a lesson many of us don’t learn romantically: If we entwine ourselves with this person, move for this person, marry this person, what should we do if things go totally wrong? What’s a best worst-case outcome? Humans seem to find it almost impossible to ask this. The Germans didn’t ask this. Stalin didn’t either when he agreed to a non-aggression pact with Germany. Few asked about worst-case scenarios before World War I.
Tom Ricks’s The Generals has a similar quality. If you have to choose between books I’d say take The Generals but they’re both excellent. Overy has a charm and flow in his writing that is difficult to convey via a single quote; for example, he writes that “Despite numerous warnings from sources even the Soviet intelligence authorities could have regarded as unimpeachable, Stalin insisted to the very last moment that Hitler would not attack. He thought he had the measure of his fellow dictator. The shock was complete.” Those sentences cascade from longer to short. The words “unimpeachable” and “measure” are somehow just right but not totally obvious. The last sentence is as short as it can be and completely evocative. Overy writes sentences like, “On the face of things, no rational man in early 1942 would have guessed at the eventual outcome of the war. In the jargon of modern strategy, the Allies faced the worst-case scenario.” The word “rational” does a lot of work in that first sentence: to unpack it here would be too wordy, but in some sense describing how that rational man turned out to be wrong is the book’s job.
Hardcover editions in good shape are cheaply available on Amazon.