The advent of the sociolinguistic institution known as a standard language no earlier than two centuries ago ushered in an immediately perceptible cultural criterion according to which the accent of a speaker that deviated from the norm acted as a barrier in rising up the socioeconomic ladder. Thus, in a well-known case, British subjects whose speech did not conform to the King’s/Queen’s English––otherwise dubbed “RP” (for “Received Pronunciation”), i. e. the accent of Oxford and Cambridge universities––were routinely ruled out of the competition for places in the foreign service and in positions of authority in government and business circles.
The American situation is somewhat less straightforward. Standard American English (“SAE”) has never been a strict speech requirement for aspirants to high office, witness the recent examples of Jimmy Carter and Bill Clinton, both speakers of a variety of Southern American dialects. For African-Americans, however, SAE is a practically indispensable vehicle in the climb up the class ladder, notably exemplified today by Barack and Michelle Obama (both graduates of Ivy League universities [Columbia and Princeton, resp.] and Harvard Law School). Not speaking in Black English is demonstrably a prerequisite to advancement in most walks of American life save the entertainment industry, where the speech of the criminal underclass may even be the norm in certain genres (like hip hop).
When it comes to foreign accents in America, there is an interesting variegation of the sociocultural picture such that racial and ethnic membership is perceived as a license to deviation from the norm. A prominent example is Henry Kissinger, who has steadfastly maintained his Dr. Strangelove German accent in English, despite having immigrated to the United States as a teenager, and has nonetheless risen to become a Harvard professor and a Secretary of State. This case illustrates the fact that as long as a person’s non-standard American speech cannot be identified phonetically with any native American dialect it need not be an impediment to their socioeconomic ascendancy.