This one is inspired by a discussion on the Mod team: A lot of historians study particularly violent periods. With violence, there is often this attitude of "I know it when I see it" but what defines violence? What is violence?
For example, does the modern state apply a different form of violence than previous political communities? Is a stateless society capable of violence on a structural level? What sort of violence does exist beyond states? Just the one between personal actors or can an institution exact violence?
Share your examples and ideas from your own study and tell us how you approach violence.
I've always been pretty fond of Hannah Arendt's definition of violence, from On Violence. She says, in essence, that violence is not, as many theorists maintain, the logical or extreme result of power, but rather its antithesis. When a state has a firm grasp on power, there is no need for violence. When power breaks down or becomes inadequate, however, violence becomes more likely. She extends this argument, as one might expect from her, to say that bureaucracies, which exist to perpetuate institutions independent of power, become breeding grounds for violence.
I don't do a lot of violence studies type stuff in my research, at least not explicitly, but I like to keep Hannah Arendt in mind at all times, and this is probably my favorite work of hers after On the Origins of Totalitarianism.