Even if you have overwhelming force there can still be casualties, especially if the local militia are slow to realize the fight is hopeless. Which can happen,

Even if you have overwhelming force there can still be casualties, especially if the local militia are slow to realize the fight is hopeless. Which can happen, especially if you take them by surprise. The locals will surely take casualties. With zero casualties for the occupying force, this may still be a negative result. Now you've made enemies of the locals, and the word will spread. Assuming your goal is not to become an oppressor you may have hurt your cause by going gung-ho into the village, even if tactically you succeeded.