 Why does the Viceroy want to overthrow the Sundans?
The sight of an Earthman on Vega III, where it was impossible for an outlander to be, brought angry crowds to surround John Crownwall as he strode toward the palace of Viceroy Tronn Ffallk, ruler of Sector XII of the Universal Holy Empire of Sunda. "We offer you partnership with us to take over the rule of the Galaxy from the Sunda—the so-called Master Race." There was even serious discussion of destroying Earth out of hand, while it is still possible. While these creatures could by no means be classed among the intelligent races, there was a general expectation, which we reported to the Sunda, that they would some day come to be numbered among the Servants of the Emperor.
 The Vegans were around before the Sundans, therefore the Vegans should be in charge of the galaxy.
 The Sundans do not understand polite society or etiquette. They really must be stopped.  The Sundans are waging war on the Vegans.  The Sundans are a race of brutal warriors, oppressing everyone in the galaxy.  The Vegans were around before the Sundans, therefore the Vegans should be in charge of the galaxy.