Like the British Received Pronunciation, General American was never the accent of the entire nation. Rather, it was derived from a generalized Midwestern accent and is spoken particularly by many newscasters--in part because the national broadcasters preferred to hire people who spoke in this way. It is sometimes promoted as preferable to other regional accents: In the U.S., classes promising "accent elimination" generally attempt to teach this accent.
General American is a rhotic accent, maintaining the postvocalic /r/ in words like pearl, car, and court. Because this is a generalized accent, certain vowel mergers, including the cot/caught vowel merger between /A/ and /O/, may be found optionally at least in informal and semiformal varieties; however, the most formal varieties tend to be more conservative in preserving phonemic distinctions.
Within American English, General American and accents approximating it are contrasted with Southern American English, several Northeastern accents, and other distinct regional accents and social group accents like Ebonics.
See also: Standard Midwestern