My first encounter with Andre Norton came around age 11 or 12 when I bought "Star Guard," a story loosely based on Xenophon's "Anabasis." It proved a rollicking good yarn. Earthlings had gone to the stars and met with a powerful empire under Central Control. Earthlings being too backward for anything else, they were allowed into the empire as mercenaries. "Star Guard" follows the adventures of a unit of mercenaries sent to serve a usurper on a backwater world. Their boss loses and they have to fight their way to freedom across a hostile world. I read and re-read the story several times, and I still have the old thirty five cent Ace paperback lovingly tucked away on a shelf in my library. "Star Guard" forms half of the book "Star Soldiers."
The other half comes from another novel I read multiple times as a preteenager--"Star Rangers." This book also found its inspiration in a historical incident (or at least a historical legend). During the decline of Rome an Emperor decided to rid himself of a pesky legion. He ordered them to march east; they obeyed; and they marched right off the pages of history. Some 6,000 years after that Emperor's edict, it is repeated by another crumbling civilization. Central Control is losing its grip on its far flung galactic empire. The Star Rangers are somewhat of a nuisance to Central Control, so it sends them off on a fool's errand of exploration. "Star Rangers" chronicles the history of this last mission.
The Central Control of "Star Guard" was very similar to the Central Control of "Star Rangers," but try as I might, I could never reconcile the dissimilarities enough to say that "Star Guard" and "Star Rangers" both occurred in the same fantasy universe.
The two stories are aimed at juveniles, their "science" is bankrupt, and they are little more than space opera. But they entertain, and that is all that they were intended to do.