So here's the first little bit of fluff for the system my guards are from:
The Void Storm Anomaly. Ringed by dead systems blasted by war and natural disasters. Only two systems are still occupied, their wardens fighting to contain the evil xeno that spill from the storm. The Warden’s supplies are stretched and their forces ragged and worn down. Still they hold.
One of the occupied zone’s is the Mahigan system. An ordinary system with four planets orbiting a yellow star, this little sun has seen war and blood shed for centuries.
The first planet is known as Ahsin, and it is a scorched world. It’s orbit brings it dangerously close to the suns fiery visage. As is remarkably common in the imperium of man worlds such as this boast significant mineral wealth. Ahsin is no exception. Mining camps dot the planets surface, it’s workers slaving under a burning sun to extract the mineral blood of the planet.
The second planet is Volundr. A Mechanicum Forgeworld, it’s almost to small to be considered a proper forgeworld. It’s factories none the less consume the vast majority of Ahsins exported minerals and spew out all the resources of life and war that the Mahigan system contains.
The third, and by far most important, world is Canadiana. Classified as a civilised world, and the only one for many light years. This is where the Governor-General rules over the system, and oversees the blockade of the Void Storm. The majority of it’s tithe is generally put right back into defending the system. This is where the Imperial Guard regiment known as the 1st Canadiana is raised and based from. Canadiana is also orbited by a small, heavily forested moon known as Taiga and contains the fortress of the DoomSeeker Space Marines. The current Governor-General and Warden of Mahigan is John Simcoe.
The fourth and final planet in the system is Autolycus. Little more then a blasted and war torn ruin, once it was a civilised jewel in the Imperium's crown. When the Void Storm underwent rapid expansion, hordes of foul Xeno brought war to the Mahigan system. It was on Autolycus that armies clashed and the wars were fought. The Imperium has pushed the majority of the xeno out, but their hold on this ruined world is still tenuous.
Despite it’s location on the frontier of Imperial space, and it’s relative small size, the Mahigan system is considered vital. This probably has far more to do with the general stubbornness of humans refusing to give anything up willingly, then actual strategic value. So while supplies are frequently stretched thin, reinforcements are regular. Frequently this takes the form of other Imperial guard forces being seconded or attached to the local defences.