I don't know. Why are you asking me? You're the author.
Remarkable how those rockets never toppled over.
Stephen Brady, commander of an Earth expedition was sent to go Where No Man Has Gone Before. But he finds, to his shock, that space is jostling with other races. Hundreds of them. And they are all ruled by the telepathic, highly organized Rihnans, who have had an Empire of sorts that has run fairly smoothly for millions of years. Brady is sure that in a very short time, Earth will be invited to join the Rihnanian Empire with a subtle "...or else" implied.
So the ultimatum wasn't "Earthman, go back," at all.