Ethan typed on his keyboard, a set of code for his virtual world. His simulation felt as real as the regular world.
He decided to make one tweak, though. Whenever a human tried to cause violence on another, that human experienced the violence instead.
Fights came to a halt. Someone punching someone else in the face only ended up hurting his own face, and a soldier shooting another person only resulted in those bullet wounds manifesting in his own chest to his death.
Ethan rigged it so that those who ordered or cajoled others to do violence likewise received that violence onto their bodies as well.
Ethan sat back as he watched his world stammer at his newfound change. Battles became immediately ineffective. World leaders engaged in wars died on the spot when their units sought to advance in combat.
He thought this would move towards peace. After the initial shock of the change, it did, but after that, new patterns would begin to emerge.
Some humans would try to provoke their enemies to make them lash out in anger and hurt their own bodies. And other humans became clever, grabbing all they could because they knew there would not be an easy way to take the stolen possessions back without violence. Some ultra-greedy wealthy people started seizing assets, knowing that without the check of violence, society could not do much to counter their acquisition.
All politicians and business leaders endured never-ending torment. Pretty much every law or policy enacted harmed another, which would result in their own harm. No one wanted these positions, but those in them could not quit, lest the action of removing themselves from office would not cause negative harm to others downstream.
Total chaos ensued, hurting those who were the most powerless, until Ethan decided to turn this off, go to bed, and think more carefully about how to best establish peace into his world. Who knew that pretty every decision any human makes connects with violence?