Actually we do have a great deal of information on how things were before the industrial revolution, as well as a lot of well documented accounts from over a thousand years ago, not only in so far as overall mortality rates go, but in how people viewed violence , its amount per population groupings and good estimations of how many died due to it. They are pretty much a matter of historic record in many cases.

Sometimes plague was even directly linked to violence as in the case of overcrowded conditions which contributed to the sudden sickness that killed off a good bit of the besiedged Athenian population (including the City's leader Pericles) during their last big war with Sparta, so one has to eaither exclude or include such considerations in one's conclussions depending on the situation.

Before the medical advances of the modern era people were in general dependent on their civiliazations only being able to achieve successfully sustained rates of personal longevity amongst all but the most affluent in agricultural times of plenty alone.

If a civilization prosperd long enough it allowed the pursuit of more sophisticated benificial technologies and situations that increased lifespans though sanitation and medical improvments as well.

When these civilizations fell, and such practices were for the most part abandoned we see populations and longevitey rates decline accordingly.

Objective modern cross disiplinarian studies have shown that enviromental factors played a much more dominant role in this than most people realize. From the sudden downfall of the anicent pyramid building civilizations of the nile and mesopotamian regions over 4000 years ago mainly cuased by a severe drought, to the falls of the Mycean, Minoin, Roman, several Chinese dynasties and several american indian Civilizations, higher levels of violence seem to be directly related to the enviromantal stressors that cuased their eventual falls.

Warmer conditions did not always mean it was good for everyone across the board eaither, often times it meant drought, flooding, and famine as well.

It all depended on "location, location, location."