I can only speak for myself, of course, but I don't have any history of abuse, not even mild; in fact, I would say that I had a privileged childhood, full of adventure. I was diagnosed with BP in my third year of college, when I became manic without any precipitating factors and was hospitalized. My moodswings throughout life have been totally unrelated to any external stimuli. I do, however, have an impressive family history of BP, going back generations (called manic-depressive then, of course). For this reason, I would consider bipolar, or the predisposition for same, genetic.

EDITED to add: After a little reflection, I think that, for me, multiple stressors can cause bipolar episodes. For this reason, I lead a very disciplined and
responsible lifestyle with as little drama as possible. I would never flirt with early symptoms...too risky.