People were quicker to violence in the Wild West days because everyone was struggling with the effects of cumulative CTE brought on by brain-rattling horse-based transport on roadless surfaces
A single mildly bumpy ride won't turn you into an NFL domestic abuser, but over the course of 20+ years? And if you were on horses or in rickety carts from the time you were a squishy infant? Boom, curdled grey matter.
No horses = no war, no murder, just pure enlightenment and peace on Earth.