In the 80s/90s, I rarely had that many kids on my block but I was always outside. I had a bike and roamed ~10 mile radius around my house. So my friends and I would just meet up some place and decide where to go.

I wouldn't say the war impacted the parental decision(s), historically kids always played outside so they were just continuing what they knew, but we kids did have safety in numbers and that's why I'd say this is a perpetuating issue.

If a parent today told their kid to go outside and play, that kid would be alone and less safe. So parents just don't allow it.

More like child services would be called and the parent charged with something. That foundational law is what prevents parents from sending out their kids nowadays.

Growing up in the 90's, there were far more kids playing outside. Even in the early 2000's, I used to remark how kids aren't getting out much anymore. Now there are articles about this phenomenon that are being taken seriously, so I guess I was right.

Don't forget the depression. The way my grandpa talked about growing up in the depression, I got the impression that kids were basically independent by the age of 7-8, out of necessity. Many of them had what could be considered part time jobs for after school and were responsible for running errands which could involve walking alone many miles from home to go shopping or drop something off.

Makes me wonder how much of helicopter parenting is caused by emergency rooms becoming probibitevly expensive?

It's the same all over the West, right? But emergency rooms are free in much of it as well.