So an interesting tidbit concerning WWII was that the military was in no state of readiness in the year leading up to it, and the responsibility to correct that fell to George C Marshall. Many of the actions he took were influenced the state of the armed forces until relatively recently and much of our success can be traced back to the philosophies which guided the policies he implemented. Sadly, he never wrote about any of that and while much has been written about that I cannot recommend anything which I could say was authoritative complete. . .However, he did write a book entitled Memoirs of My Service in the World War.
Highly recommend.
Also, though it is a bit longer than your specifications, and slightly outside the purview of the world wars, The Seven Pillars of Wisdom is always worth a read. Especially if you want to understand guerilla tactics and asymmetrical warfare. As hard as it might be to believe, it is even better than Lawrence of Arabia -absolutely no disrespect to the masterful David Lean.
Now these are close to your subject matter, but outside the parameters you specified for length. First, is The Rise and Fall of the Third Reich. I would not take everything in it as gospel, and where you find discrepancies between what is stated and what is commonly accepted, I would say look it into yourself and you will never feel as though your time and efforts have gone unrewarded.
I am less knowledgeable about WW I than I am about pretty much every other period of American history, but a book which I have found problematically unreliable but still really insightful, is The Illusion of Victory. There is some powerfully motivated reasoning going on, and I suspected some cherry picking of information as well, but there is also some extremely underdiscussed aspects which he touches upon which make it worth the read. It will complicate your feelings on that topic and that is always good.