There's an underlying care instinct that needs to be activated. Its emotional; you can't explain it, they have to experience it.. There was a post years ago supposedly describing the empathic awakening of a white supremacist, which occurred as he was waiting to harm or harass a father and son on a bus, and the moment of awakening happened as he witnessed the father expressing his love for his son and something clicked for him, probably because he wanted that sort of affection from his dad and never got it.
complex trauma is due to many smaller events occurring over a long period of time, usually during childhood but also during a relationship. "serious" traumas are not necessary
And indoor plumbing!