I think my daughter's BPD might be connected to trauma due to my instability when she was younger, and my divorce from her bio father, who never tried to maintain contact with her, but professionals are now saying that BPD may be genetic. I am in a group for parents of BPD kids and I have asked about background (divorce, separation, instability, deaths, etc) and while there are more divorced parents, there are also many who are both biological parents, with no problems of stability.
https://www.sciencedaily.com/releases/2008/12/081216114100.htm
But my daughter also showed signs of what would be called Oppositional Defiant Disorder nowadays (not recognized then) from as young as 2, which seems to point more towards a genetic disposition for BPD.
We had a vicious circle. The more she acted out, the less I could handle it, so the more she acted out, until she was regularly coming after me with knives and I was on serious psych drugs to deal, making me less capable as a parent, making her feel worse and attack me more. Year of this, until she was in her early 20s. She had gotten great therapy and put in a lot of work, and has really changed her life, but the BPD demon still tries to pull her down.
I had asked her if there was any other trauma in her past that maybe I don't know about and she said no, nothing ever happened., but I can seriously see how BPD and trauma are related.
Here's a good chart I use to help people see the similarities: