Diplomacy and Time Distortion
The time distortion that is so common with warp travel is a source of much consternation within the Imperium, especially the Imperial Guard. It is often the case that a punitive force will be assigned and dispatched to quell a rebellion on a planet, but due to the difference between the passage of time in the immaterium and the materium, they all-too-often arrive years, if not centuries late. The rebellion will often have been stopped by more local forces by this time, and the Guard taskforce will have no need to attack.
Needless to say, on a warship full of troops that have spent months of their time preparing for a war and working themselves up into the all-too-common battle-frenzy, this news is not always taken well. There are many instances of "misinterpretation of orders", or "communication problems" between planet and ship in these instances. This conveniently allows the Guard to invade the "rebellious" world and prosecute the war they have spent their time preparing for, and lets the ship captain eject a large group of increasingly aggressive soldiers from his ship.
The inevitable defence or counter-attack from the planet only serves to reinforce the Guard's belief that the world is rebellious, and such a war rarely ends well. If the Guard is defeated, the planet is listed as rebellious again, for destroying a task force of the Imperial Guard. If the Guard are victorious, the planet is subjugated anew, and the anti-imperial elements will gain support, making the planet much more likely to actually rebel again.
What follows is the account of such a situation, specifically involving the Ramoran 81st and the planet Horenta.
In a small system, consisting of barely half-a-dozen planets, only one of which was inhabited, nothing was happening.
Naturally, things did not stay like that for long.
The blackness around the fourth world in the system, which the inhabitants of Horenta, the only inhabitable world, knew as "that big one with the rings", bubbled. This was not a normal thing to do, and, had anyone on Horenta been looking at the space instead of digging, it would have been at least the second largest news story of the day, next to the announcement of the annual pay bonus, or lack thereof. In true Horentan fashion, though, no one paid a piece of space any attention. It wasn't like it was going to go anywhere, they would have said; we can always look another time.
Out of the bubbling, there emerged a shape. It was not shaped like a piece of mineral rock. This was the best description that the Horentans could come up with, rock being the only significant feature of their planet.
Instead, it was vaguely rectangular, with a great, shovel-like prow on the front, and a sputtering tongue of fire emerging from the rear. If the Horentans had possessed a telescope powerful enough, they would have seen that it had thin spires and antennae emerging from its sides, as well as depressions that looked worryingly like weapon batteries.
The shape, which was, in fact, an Imperial Battleship by the name of the Cleansing Flame, quickly entered orbit around Horenta.
Actually, this is not entirely true. It took the battleship three days to enter orbit around Horenta. This amount of time was not due to the battleship's speed, but instead to an unfortunately-timed comet, which the battleship was forced to manoeuvre around.
When, finally, the battleship did enter orbit, some of the Horentans noticed it. They did not notice it because of its extremely large presence in low orbit above the clear Horentan sky, but rather because of the incessant, and very loud, vox hails that the battleship broadcast.
The few Horentans that noticed the battleship were, inevitably, not the ones in charge. They were workers at a small vox-broadcast station in Horenta's main city, if a few hundred small stone buildings could be called a city. There ensued a few days of mild panic while the workers tried to get the leaders of Horenta to pay attention the them, and to stop searching for any positive numbers in the annual profit reports.
Eventually, some of the Horentans got sorted out, and a reply was pieced together, asking what the battleship was doing, and if the crew would like to come down and spend some money.
At which point the battleship informed the Horentans that they were all rebellious heretics, and they would be duly cleansed.
The Horentans, naturally, were a little perturbed by this turn of events.