Both dissociation and fight response (anger, rage) connect to trauma. The "why" can be almost anything that triggers anger for you or stress overload. Doesn't even have to relate directly to the trauma, but to the way your body feels stress and anger. But working through the initial trauma, recognizing when triggered or overloaded, and also on how to cope with stress, will likely help gradually.
I don't tolerate anger in myself well. I just direct it back at myself. So sometimes I've dissociated and just gone totally numb/blank (actually more common). Other times I detach and rage against myself (self harm). I don't direct it outward, but it's really the same thing. My mom was abused as a kid and her anger was directed at me (sure she was dissociated herself because of how she looked and acted). Had she done some sort of therapy for her own trauma, that would have been great. She'd be under stress, but then just snap over some confusing last straw and totally lose it (screaming, but also hitting, throwing, breaking things...quite scary for a kid, but now I understand it as most likely a negative result of her own CSA that she never got help for). I think because of her I just learned really early to turn my anger inward. But it's still raging and difficult to manage sometimes. And self destructive. Therapy is key. But then also noticing when you start to enter these states, and how you can de-escalate through walking away briefly, taking a break, setting boundaries where needed, etc.
