Odysseus Ascendant: Odyssey One 7 by Evan Currie
Series TL;DR: This series does an excellent job world building and the space combat is excellent through the sixth book, and even through most of the seventh. This last one performs a mildly foreshadowed ass pull that allows Earth to threaten a Samson maneuver which causes the Empire to back off. Then the series stops. The world building has been relatively convincing, which makes it a shame that the series has not been directly continued. There is a related two book sequel series focusing on a more charismatic character, but it peters out and does not seem to draw to a good conclusion. I don't sympathize with the MC, or most of the characters with primary agency. For me that happened around book 4.
TL;DR: They make peace with Odysseus in time to detect the entire Imperial sector fleet heading to Priminae home world. They ambush it and pick away at the massive numerical advantage (over 400 ships versus 20-40), making them go more slowly. They pull out the stops on various weapons, especially their willingness to use anti-matter and missile/projectile weapons gives them a large, but not insurmountable edge against the Imperial sector fleet. In reaction, the Imperials realize that Earth has been putting backbone and trickiness into the Priminae. So if they eliminate Earth they can reduce the threat. So they do, and the fleet is forced to teleport directly into combat, and then they use their deus ex machina to blow up the sector fleet home port, and force a retreat. And then the story runs out, leaving the setting in a volatile place.
In this case, there's not much set up before getting into the plot. The sector military governor decides to smash the threat because there are internal affairs to worry about. He refits the ships with extra armor, looks over the data and goes for it.
Their first thrust is to go after the colonies in a straight line for the primary Priminae world. And they do. The size of the fleet makes their gravitic and tachyon signature easily detectable, since it is actually larger than the Drasin horde. The sector governor wonders why the directives came down to go after the Priminae so hard, and why they opened with the Drasin, which destroy garden worlds. None the less, he has a threat in his sector and he will worry about cleaning up behind up after he's done with the task in front of him.
The Earth faction pulls out all the stops, effectively making a competition of ways to deliver outsized amounts of anti-matter to the Imperial ships. They figure out grav mines to slam into the leading Alcubierre sink and increase the mass of the sink, hopefully creating a singularity and sucking the ship in. They figure out how to run drones behind a modified Archangel fighter to hit the ships. Fighters are much smaller and shorter ranged than the parasite craft, and are hard to detect and quick to move making them hard targets to hit.
They maul the incoming fleet for very few losses, continuing to withdraw towards the Priminae core world. However, the imperial fleet decides to change tack and goes after Earth on the theory that Earth is the backbone behind the new innovations and improved tactical and strategic sense. This catches the defending fleet off guard. And in a place where they don't have teleportation, the empire would have an insurmountable lead.
As it stands, Earth is stuck with a laser constructed and directed by the united command and constructed using tech scavenged from the Drasin horde. It takes out a huge chunk of the fleet, but it's not enough to stop them. The Imperial fleet is sitting over 30% casualties, and hasn't broken (mostly due to an approach to discipline similar to propagandized CCCP commissars).
The array is destroyed, but they've figured out how to enable a teleporting "laser" powered by a significant portion of the output of a sun.
The MC teleports directly into a Lagrange point with the entire fleet, losing a few ships in the process, and then fights for a while.
It's not enough. So he's handed control of the teleporting laser and uses it to burn the home port of the Imperial fleet and broadcast it. He then threatens a Samson maneuver. "Yes, you'll kill me (or my planet), but I'll destroy you too." Effectively MAD. I'm going to use this to render as many planets and bases of yours useless as I can while I run.
The leader of the imperial fleet expresses skepticism, and the MC burns one of their ships to prove his ability.
The Imperial fleet withdraws with an effective Mexican stand off.
Basically, the Imperial fleet is going to try to hunt down and either obtain, or destroy the teleporting laser. In the mean time things are in a stalemate.
The entire sentient planets thing is put on hold, and since this is the end of the series, never addressed again.
Does the Earth survive? Not fully answered. There are sequels, but they don't seem to do the same thin.
My guess: I think it was a planet that got miffed at the other planets and decided to trigger of the planet destroying war. The point was to destroy the sentient planets. Everything else fell out from that. Not that this will ever be answered.