Sorry for the title gore. I suppose if my question doesn't make sense to you, please answer me this instead: When did modern American English develop, and what are the similarities and differences between it and old English?
hi! fyi, you'll find a few previous posts in this FAQ section
As you'll see in those threads, the differences between Old English and modern American (and every other variety of) English is extreme. But on the off-chance that your last question is asking about the divergence of British and American Englishes, there's another FAQ section that may be of interest