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.