I am a millennial who grew up in the 90's when spanking was still around but steadily declining in popularity. In the early to mid 90's my parents spanked our bare bottoms but largely stopped doing so by the time the late 90's came around. It feels like social attitudes towards spanking shifted pretty hard during my very childhood and I wonder if my generation may be the last where most of us know what a sore bottom feels like. I suspect younger generations won't relate.
While I did get spanked as a kid, I know that what I experienced is nothing in comparison to previous generations who grew up when bare bottom spanking was the norm in most households and even commonly administered by authority figures other than one's own parents (such as teachers, babysitters, etc). There's no doubt that baby boomers were spanked much harder and more frequently than Gen Xers who themselves were spanked harder and more often than us millennials and so on.