As this Reddit comment explains:

This. Earth/Sol controls a huge region of space but hasn’t fought a war in decades, maybe centuries, and rests comfortably on its laurels. Meanwhile, the main character lives in and serves a distant star kingdom at the junction of multiple wormholes, contested by an even further star empire. Eventually the two nations agree to end their 30+ years of grueling darwinian warfare and team up against Sol, bringing all of their technological and tactical advances to bear. The result is such a curbstomp that the author had to search for ways to stretch it out over any more pages than the travel time required. It’s like The Final Countdown, a modern nuclear supercarrier going up against WWII fleets.