Humanity Rising. The Skyward Saga, #5

Earth is under overwhelming assault, and Kaishi has arrived to lead her people, just in time to see them destroyed. Hiding under the mountains with continuous attacks from the skies, Kaishi marshals humanity's remnants in a final stand against overwhelming odds. Hope resides in a last ditch effort to call out beyond the stars for help, as Kaishi climbs the cliffs to fight one final time beside her friends.
Sax is in similar straits, uniting with other rebels in a strike at the very core of the galaxy, to a planet few are allowed to see, much less set foot upon. There they must try to find a weakness, a way to expose and end a millennium-spanning plot to control the galaxy's sentient species. HUMANITY RISING is the fifth book in THE SKYWARD SAGA, a sci-fi adventure series that puts the galaxy at risk as whole species wage wars for survival, worlds are ruined in revenge, and histories are rewritten by the victors.
If you like fast-paced, action-driven science fiction with a new twist on the alien encounter story, you'll love A. R. Knight's HUMANITY RISING and the entire SKYWARD SAGA.