The Last World War — Dayton Ward

It started small, with an unprepared band of Marine reservists encountering deadly extraterrestrial visitors in the backwoods of Missouri. But this fatal First Contact rapidly escalates into a global crisis as mankind discovers that two warring species of aliens have invaded our world through a network of hidden interdimensional portals. The apocalyptic conflict between the hastily labeled "Blues" and "Grays" has already devastated their home planet. Now Earth has become the final battleground in a cataclysmic war whose origins are barely understood.

Forced into a hasty alliance with the alien Blues, humanity has no choice but to brave the awesome Gray onslaught in every corner of the Earth. From the mean streets of Atlanta to the mountains of Afghanistan, from Washington, D.C., to the alien's war-torn homeworld, all of humanity must unite to survive.