Why does the remnant faction attack a planet?

Why is the remnant faction bombarding a planet?

Its surviving warriors are reacting to a leadership strike that also destroyed their species' reproductive caste.

The fictional empire's leadership and reproductive caste occupy the same centers. Destroying those centers therefore removes its ability to reproduce as well as its command structure, making the decapitation strike genocidal in effect. The surviving warriors' anger helps explain why they now behave differently from the enemy encountered during the earlier war. The moral argument remains contested: the empire runs on slavery and aggression, while its opponents regard an abhorrent attack as their remaining way to end the war. An analogy with the decision to use atomic bombs against Japan frames the problem of choosing an abhorrent action to end a war. It is an interpretation of the strategic dilemma rather than a claim that the cases are identical.