Star Trek The Original Series: The Captain's Oath by Christopher L. Bennett
The 'Star Trek' bookverse is in flux, there are less of them and the new publisher seems to have switched to trade paperbacks. After a couple of unbearably dull books, comes this enjoyable book.
This seems like a collection of short stories and vignettes that act as a prequel to 'TOS'. This tells stories of Kirk's commands before he became captain of the Enterprise. He rescues endangered civilizations and grapples with Klingons. He defines himself as a leader and earns fame and adulation. We see Kirk and Spock on the way to becoming friends and cultural icons and arbiters of moral authority.
“Vanished into galactic history.”
“Intelligence and social systems capable of a galactic threat;”