How do you quantify peace and violence?

The idea that modernity is the most peaceful period in human history is one I'm very skeptical of. It seems to mainly come from Steven Pinker's "Better Angels of our Nature", which is not the most highly praised book I've ever read. I don't want to get into too many details there, in part because it's probably not the direct impetus to OP's post, but I would like to point out that there are some major difficulties with this sort of claim. First off, historical data is very limited. It's amazing how much we can learn about the past, but it's important to remember that it's usually not even a fraction of everything the past actually comprised. For most periods in history we simply couldn't begin to make an assessment of quantifiable violence, so to make comparisons across history of a phenomena that we can't even quantify consistently (or at all, in many cases) comes off as ambitious at best. In Pinker's case, I'd call it more like wishful thinking. Secondly, violence itself resists such analysis. Even if we had standardized, reliable, census-style homicide/assault/whatever rates recorded in a convenient medium for every society throughout time, how do you go about assessing which is more or less violent than the rest? It's essentially a value judgement that ends up only mirroring your biases.

Steven Pinker addresses this in his book "The Better Angels of Our Nature". Anthropological data from contemporary hunter-gatherer societies and archeological data from ancient ones indicates that they are by far the most violent societies to live in. In some cases, as many 25% of males could expect to die violently, and if ongoing warfare between a nearby group broke out, this could temporarily climb higher. Take the worst year ever from the worst inner city ghetto in the US, and it never came even remotely close.

It's an amazing book, and worth reading if you're interested about this subject.