Regional accents develop within countries, never mind between nations separated by thousands of miles of ocean. Therefore, just as accents and commonly used expressions vary from one region of England, or of the United States, to another--so the accents and commonly used expressions differ as between England and the United States.
A significant difference is in spelling.
This page (click here) gives a biography of Noah Webster. Webster was a school teacher in the United States, who felt that American children should be given a simplified spelling for words in what was as much their language as it was anyone else's language. Therefore, Americans write "center," "color," "humor" and "honor" when the English write "centre," "colour," "humour" and "honour." However, for all the slighting remarks the English may make, they have adopted some of the simplified spellings which Webster proposed. For example, all people in the English-speaking world write "magic" rather than "magick," and "music" rather than "musick."