Why Do We Speak American English (our dialect of it) Rather Than British English?

[wasd]

I was just thinking about English because we're kinda in English right now. Perhaps it would have been better to ask why we speak dialects before asking this question, as answering this question that I think I now know the answer to now that I think about why we speak dialects should be easier. (I like run-on sentences, unless they're used in writing, or on a formal occasion).