The point of invasion has been to kill people until the other government will do what you want. "Kill people" is supposed to be just the military, but there are inevitably civilian casualties. A big part of the point of a military (namely defense) is to keep anybody else's military from getting inside our borders, where it's our people being killed.

Both snidane and I assumed that there would be danger to civilians in case of an invasion. The invader doesn't have to intend genocide for that to be true.