If you've not listened to Dan Carlin's 6-part series on the Great War, take the time to do so. The "whys" and "hows" of World War I are much harder to get your head around than WWII...it's just much less linear. Not only does he do an excellent job of making the mechanics of the war understandable, he draws the element of humanity into stark relief by interspersing explanations of troop movements with first hand accounts of the suffering and carnage men sustained.
Episode IV focuses on Verdun and can be listened to as a stand alone episode but the rest of the series is very much worth the time. http://www.dancarlin.com/product/hardcore-history-53-bluepri...