I was having a debate with a friend over how an accent comes to be.
He argued that the language that a group of people would speak would shape their voices into what we would call an accent. That the reason we American's do not share our British founder's accents is largely due to all of the immigration to America, that after mixing every nationality in the world, you were left with what we know as a typical American accent.
While the idea of a multitude of accents mixing to create one sounded plausible, and the fact that a language would play a large role in the development of an accent sounded credible as well, I couldn't quite accept it.
I countered with the fact that the Irish, Scottish, and British all speak English, but they have differing accents. As far as I know, those three countries were not impacted by immigration as much as America, so I don't see that as an answer to the question. Then I went back to the topic of American accents. The Northern and Southern hemispheres of America have completely different accents. Within that even, different states sometimes have different accents. I live in Wisconsin, and whenever I travel to a state far from my own, people point out that I add an emphasis to my "O" sounds. Then you have some of your typical Boston accents and such. The list is far from short.
Now I understand the fact that you pick up the accent that you grow up around, but how did all of these accents originate? While the language and immigration theory seemed like the answer, how did all of these "mini" accents, so to say, pop up? What during the course of history shaped the way we speak?