How did the American accent form?

Most American accents are rhotic, yet there are still many rhotic accents in the British Isles, which themselves are all distinct from each other. To suggest an American accent is the untainted 'true' English accent yet somehow every other has changed including Canada, Australia, New Zealand etc is clearly some kind of Yank delusion. I'm not saying any Americans on here believe this but some seem to.

Can you distinguish between LA or even So Cal accents? I lived there for 5 years and couldn't decipher a difference from say San Diego to the Hearst castle

Likewise there seems to be people in both the US and the UK who think British accents are unchanged and that only American accents have diverged/"been corrupted".

It sounds like the trashiest southern English accent possible

I've lived in LA/OC all my life, so I can distinguish parts of those counties, but I'm not familiar with SD accents. Honestly, the differences are extremely subtle, and most people can't distinguish them. People move around a lot, which adds some difficulty. For example, I lived in OC for like 8 years, and my accent is more similar to OC than to LA, and it's pretty different from that of the neighborhood where I live. I didn't really think about it too much until my mother commented on how I "talk weird," and my father informed her that my accent sounds like OC.

>The only unaccented American voice is that of the Bostonian
You're certainly right about that now, we have so many fucking transplants and college students that the Boston accent has basically all but died out aside from parts of Southie and certain suburbs. Pisses me off sometime desu.

Honestly we're just mid westerners who say soda instead of pop.
Hollywood is full of transplants.

Canada's accent is closer to American than the rest of the Commonwealth

I think it’s mostly just because people heard that the London accent was a manufactured accent from the Victorian era and wrongfully assume it applies to the whole isle

If you mean RP yes it is a mostly manufactured accent that private schools enforced on the upper classes