Washington's Dirigible by John Barnes

The war for a million Earths spreads to an alternate eighteenth century in the second book of the epic science fiction series the Timeline Wars John Barnes has reinvented alternate-history science fiction in his ingenious saga of the battle to save the multiverse from enslavement by an alien enemy who can transcend time and reality. In the second volume of his remarkable trilogy, the war moves to a new battlefield: a different colonial America still happily tied to the British crown, where miraculous machines prowl the skies. There are a million different Earths across an infinite number of timelines'??and every one of them is in peril. Former Pittsburgh private investigator Mark Strang is now a fully trained and blooded Crux Ops special agent, dedicated to the fight against the alien Closers who are invading every Earth in every time. Now the eternal struggle is carrying Strang to a different 1775 Boston, home of astounding technologies, where the colonists remain fiercely loyal to their king across the ocean. Something is rotten in England, though, and Strang must ally himself with the well-respected commander George Washington, the Duke of Kentucky, to derail a terrifying Closer plot and put this world'??s history back on its proper course. But the enemy has unleashed a secret weapon that could permanently shift the balance: an unstoppable agent of destruction . . . named Mark Strang.

This book is part of the "Timeline Wars" series.
Here are some other books from this series: