Mark Twain (+1910). He spoke English, and that in the United States.
The varied manner in which various folks pronounce and speak the English language across the United States and Canada, is, indeed, a rather fascinating study. We all know the unique drawl of the aristocratic Southern accent, or the Wisconsin "O," or the distinctive sound of the New Yorker or Bostonian. Certainly it is great to have an account of what those differences are, where they are to be found, and, at least in theory, where they come from.
In this post, I wish simply to provide a couple of links to relevant and, in my opinion, useful, sources.
The dialect map from the website linked immediately below.
Recently, I happened upon this site, which includes not only a detailed map, but links to dozens of youtube videos featuring folks speaking with the accents proper to their locality: http://aschmann.net/AmEng/
Once such video is that of these Tangier Island, Virginia, watermen:
This site includes accents of English from outside the North American region, as well: http://www.dialectsarchive.com/north-america
Here is a project from the University of Georgia: http://us.english.uga.edu/cgi-bin/lapsite.fcgi/
This link takes you to an atlas at the University of Pennsylvania: http://www.ling.upenn.edu/phono_atlas/home.html
Here we have a PBS attempt at the subject, and including a little quiz: http://www.pbs.org/speak/seatosea/americanvarieties/
Finally, here is a link to a book on the subject of the development of the language, this by H. L. Mencken, The American Language, published in 1921: http://www.bartleby.com/185/