History tells us that the prestige that a regional variety of a language acquires depends not on the intrinsic merit of that variety but on the political and economic power that the users of that variety manage to acquire and the extent to which they can socially dominate over the users of the other varieties of that language.
During the reign of King Alfred (871-901), the dialect spoken in the south-west of England was the most prestigious dialect of English. After the Norman Conquest, London became the most important political and commercial centre of Britain and during the fifteenth and the sixteenth century Oxford and Cambridge became the most important centres of intellectual attainments in Britain.
Because of all this, the dialect spoken in and around London, Oxford and Cambridge became more important than the other regional varieties of English and ultimately acquired the status of Standard English to be used all over Asia and Africa.
Will American English also surpass British English as the dialect spoken in and around London, Oxford and Cambridge surpassed the variety of English spoken in the south-west of England? A stream, says a proverb, can never rise above its source.
Will the metaphorical content of that proverb be proven false in the case of American English? Time alone can answer such questions. What is certain is that the English language has gained enormous strength and vitality because of its use in America.
If English has turned out to be the most widely used language in science, technology, international trade and international diplomacy, it is partly because of America being a superpower in the world of today.
Its use in America has added a large number of vocabulary items and locutions to its stock. American authors like Thoreau, Emerson, Whitman, Frost, Hemingway, Faulkner, Steinbeck and others have only enhanced the literary prestige that this language gained because of authors like Shakespeare, Johnson, Wordsworth, Shelley, Keats, Yeats, Shaw and Forster.
William Archer has said about the enormous vitality that English has gained because of its use in America.
We are apt in England to class as an Americanism every familiar or too familiar locution, which we do not happen to like…. But there can be no rational doubt, I think, that the English language has gained, and is gaining, enormously by its expansion over the American continent.
The prime function of a language after all is to interpret the form and pressure of life the experience, knowledge, thought, emotion and aspiration of the race which employs it. This being so, the more tap roots a language sends down into the soil of life and the more varied the strata of human experience from which it draws its nourishment, whether of vocabulary, or idiom, the more perfect will be its potentialities as a medium of expression.