PTSD:

When one is traumatized and put into a modern area, one might go "crazy".

After listening to a TED talk by a speaker named Sebastian Junger, he said after coming home from war, he felt so alienated with modern society, he couldn't handle it.

When 9/11 happened, everyone was traumatized,  therefore, the crime rate when down, the suicide rate when down, the murder rate. That's because everyone went through this trauma and came together and supported one another.