Star Soldiers is a compilation volume of Star Guard & Star Rangers.
I was always more fond of Star Rangers than Star Guard even though they are 'very' loosely related. Both have a Central Command.
In Star Guard humans went to space and found that they weren't even second class citizens they had to become mercenary soldiers. It's a good read (No Andre Norton is exactly a bad read) but I prefer Star Rangers.
In Star Rangers a vessel of the Stellar Patrol crashes on a planet way, way of any known charts. They explore and find a city of high technology occupied by refugees from a passenger liner. They are being dominated by a ruthless telepath.
After many perils the depose the dictator in the process discovering the name and origin of the planet. I won't spoil the suprise you'll just have to read the book.
Having many of Andre Norton's books in single volumes it is nice of Baen Books to bring back these old classics. Gives me a chance to replace all the tatty (tatty through over-reading)copies I have.