Really, in just the last 80 or so years, our language sounds immensely different. They did not use contractions as often as we do now. And, as Jay pointed out, we tend to slur similar sounds, like mixing up the sound of the T and D, soften the Rs, and don't define the differences in our vowels in many cases.
In Alabama, when a politician is elected and sent to Montgomery, I've always noticed that they start speaking differently. It is an area where the majority still speak an antebellum version English, slow, pronounced vowels... it's very rhythmic but slower than the way most Southerners speak.
I grew up in North Alabama, where we spoke something closer to mid-Atlantic... Think Cary Grant, even Don Knotts. This was a Warner Van Braun region, more international, because of NASA and the Arsenal's Nuclear arms race. But, the rest of the state would say that we spoke like Yankees. And, when I would leave the state, people assumed we were from California, unless we were actually in California.
But, of course, the more rural you get, the more stereotypical accents get. You could actually place where people grew up in the state from talking to them for just a few minutes. But, lately, everyone is becoming more enmeshed, except Montgomery. For some reason, I think that when people move there, they practice their speaking with mouths full of marbles.