Tides of Darkness, by Aaron Rosenberg, follows the events of the second war. Basically a novelized version of Warcraft II: Tides of Darkness, this books shift perspective from the two sides of the conflict.
The Orcish Horde, now led by Orgrim Doomhammer, seeks to seize all of Azeroth in hopes of returning its people to a life of honor and prosperity. The native inhabitants of Azeroth, however, will not roll over without a fight. After the fall of Stormwind, Anduin Lothar, former champion of Stormwind, seeks the aid Lorderon and the other human nations - out of necessity, the human nations forge an alliance for the very survival of their race.
As the two forces vie for dominance, other native races become engaged in the conflict. After receiving aid from the Horde, Vol'jin, leader of the Darkspear trolls, allies himself with the Doomhammer, lending their might to the already imposing force. Meanwhile, the dwarves and elves soon ally themselves with the human alliance as it soon becomes apparent that their survival hinges on the defeat of the Horde.
Tides of Darkness follows the events of The Last Guardian and Rise of the Horde, if you're interested in this book I suggest you check out those first, both of which are great reads and will add to your enjoyment of the story. This is a fairly quick read, and worth the time if you're a fan of the Warcraft universe. If not, however, I doubt you'll find it too compelling. Rosenberg does a good job of setting the events of Warcraft II to literature, but it feels as if he was aiming for younger audience with the book, which consequently, alienated me a bit from the story.
tl;dr decent book, check out if you love Warcraft - if not, pass.