The Last Tyrant — Peter Bostrom

Change is coming.

Legendary American Admiral Jack Mattis, thrown into an unfamiliar universe, must now confront the impossible and do the unthinkable in a place very different from his home. New alliances must be forged in the face of powerful new enemies. Strange technologies may hold the key to victory, or hasten Earth's demise in all timelines. Change is coming and the howling winds of war at his back will drive Admiral Mattis onward toward a final confrontation.

One thing is clear: The future is mutable, changeable, malleable. Or is it? Are Mattis's and Earth's destinies set in stone? Dark secrets will be revealed, terrifying enemies unleashed, and through it all, the true face of Spectre looms ever closer.