Britain
wasis a shitshow of accents across the country and continued to change drastically more.
This is still a thing and is only just about fading.
For an idea of how varied British accents are: My family moved to the UK when I was a kid. I have three siblings, with a 7 year total difference between the oldest and youngest of the four of us, so all about the same age.
We have noticeably different accents.
Why? Because we got divvied up into different schools due to placement availability when we arrived and went to different secondary schools (middle school+high school combined). Our accents range from MLE (no “th” sound - “my bruvver - ‘es a bit fick, innit”) all the way to “posh” accents you’d expect to hear at an exclusive private school.