THE TERRAN PRIVATEER is the first novel of the DUCHY OF TERRA series by Glynn Stewart. I am already familiar with Glynn Stewart due to the fantastic STARSHIP'S MAGE series. That series was about magicians able to move starships through hyperspace. This is a more grounded series about the idea of Earth making First Contact with an expansionist alien race, only to be swiftly conquered. Which is quite the hook.
STARSHIP'S MAGE is a book that has been sitting on my Kindle for some time and I am kicking myself for not reading it sooner. It is a book that I strongly recommend on the basis of simply being a fun read that provides a simple but consistent space opera setting. I have some issues with the book (technically omnibus of four novellas) but it is, overall, one of the better things you can pick up on Kindle Unlimited.