Answer: it's only been in the last few decades that we've been giving people with "issues" powerful psychiatric drugs and then letting them loose on the street. In prior ages, they would be kept locked up or under close supervision.
Why have most of these tragedies only occurred recently? ,, Repeating firearms have existed for over 150 years the Colt revolver for example. ,, Why didnt those kinds of massacres occur 150 120.. 100 years ago?
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There were mass killings, many of them. Wild towns and cities on the frontier with angry wars beteen peoples. Mass killings of indians and settlers, mass killings of criminals on rampage, masss killings of people being robbed, whole train full or wagon train ful.
You just dont have enough informaion.