Read this one about six years ago - I highly recommend it. I've mentioned this before, but Macmillian and Kennedy read this just before the Cuban Missile Crisis kicked off.
Had to read her "The Zimmerman Telegram" in high school, finally got to this one late last year. Massive in detail, definitely NOT light reading: will require your fullest attention, but worth doing. The first chapter, with the crowned heads of Europe at King Edward VII's funeral, is alone worth the price of admission.