The German Language

[abaris]

After the American Revolution Americans may have felt a need to distance themselves, just as a child feels a need to distance himself from his parents by doing things differently. Then when the child becomes an adult, he can face the parent as an equal so there’s no more need to rebel.

That's giving them too much and too little credit. Dialects simply developed in certain regions. Probably over a very long time, way before the revolution. Nothing political about it, just people talking to each other and developing a particular way of speaking. People sound very differently in the deep South than they sound in upstate New York. And even that is simplistic.