Could it be Harry Turtledove's Out of the Darkness by Harry Turtledove? The cover seems to match your description. It was published in 2005.
THE CLIMACTIC CONCLUSION OF A WORLD WAR
As the Derlavian War rages into its last and greatest battles, allied nations maneuver for advantage over one another in the postwar world. But before that time can come, the forces of Algarve, Unkerlant, and their allies must clash a final time, countering army with army and battle magic with ever-more-powerful battle magic.
In the midst of it all, the people the war has battered and reshaped must struggle to face their greatest individual challenges, as loves are shattered and found, terrible crimes avenged...and some journeys end forever.
Nor will the end of war bring lasting peace...
