[member="Darth Carnifex"]
Of course, and an all out attack and battle is fine and I wholeheartedly approve. However specifically targeting the civilian population with the intent to kill or to purge hardly seems like the way to conquer a world, do to a few reasons:
1) It destroys any level of sympathy of trust between the population and you, requiring a tighter military grip to keep it controlled and under your rule
2) If the destruction of the population is complete, you need to bring in your own colonists to make the world profitable again.
3) With the amount of death and carnage, and the type of weaponry used so far, you're destroying what little infrastructure there already is, meaning you need to invest even more into making the planet viable.
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In Conclusion: You are damaging what you intend to take, creating antipathy for your faction, and providing no clear goal or grounds as to why the system should rebel to your banner and hail you as their rulers, in fact you are providing quite the opposite, and giving just about every other faction a very good reason to attack you for what you're doing.
Complete Side Note: We're already dealing with terrorism in real life, it's ramping up by the day. Do we really want to promote this kind of activity in the world?