Why did the English language change in America?

Answer 1

Assuming you really mean "why" and not "how," the answer is that all language changes with use. American English is surprisingly old fashioned compared to its British cousin because transplanted linguistic communities are conservative, often retaining old forms and meanings that become extinct in the Mother country.

Native speech and the proximity of French and Spanish speakers offered some small change to the vocabulary of American English, but the greatest external agent of change has been the dialect of the African slaves, now known as Black English or Ebonics.