Sorry if this is the wrong subreddit, someone please correct me if there's a better place to post this.

So where did the American accent come about, and why is it so wildly different from other accents? Accents such as Australian, South African, and to a certain extent, North-east American accents tend to have a closer relationship to British accents than American accents do. For example, very hard "R"s and pronunciation of the letter "A" especially. I can't think of any other accent off the top of my head that has that same hard "R" sound that most American dialects have.

So is there any real origin of the accent, or was it a natural evolution that just differed from other colonies?