My father's family had five kids (all boys) and their parents were extremely abusive. Emotionally, phyically, verbally. My father's father was an alcoholic, and a misanthrope who left my grandmother to deal with all those kids by herself all the time. She used to line them up and paddle them one by one every day because she "just knew they'd done something to deserve it."

They did not have a happy family.
My mother was an only child. Her mother was seriously f**ked up as a child, and carried a lot of emotional baggage into her parenting. My grandfather was essentially a very gentle man, but he had to deal with my grandmother and my mom, so he lost his temper a lot. My mom was spanked occasionally, but most of the behavior in her house was driven by shame and guilt.
They have five kids, me, then my sister Andrea 2 years later, my sister Catherine 4 years later, my brother Ben was born 3 years after Cat, and my sister Aimee was born 4 years after Ben. I was 13 when Aimee was born.
When Andrea and I were little my parents both spanked as well as shamed/coerced/etc. It was pretty awful, to be honest.
After Catherine was born, two things happened: 1) my Dad got sick and had to leave work to stay home with the kids, and 2) my mother started working at a very progressive preschool as a teacher. My mom was pretty deep into LLL at the time, and so they were already cosleeping and bfing, as well as doing general attachment-style parenting with Catherine. The preschool did not allow the teachers to utter the word "no" in front of the kids. They were very GD, and sent the teachers to seminars on classroom management and GD. My mother realized that this was the kind of thing she wanted to do at home, so she never spanked again.
Eventually she convinced my father that spanking was wrong. So essentially they broke the cycle of abuse themselves, and more power to them.
It was a good experience for me, I think, because I saw them raising my younger siblings without violence, and vowed that I would do the same with my own children.
They did continue to punish, and that's one thing I am trying hard not to do, but overall I think they did a good job of overcoming their childhood traumas to really become good parents.