When British colonists made their way to the New World and established the first permanent settlement in 1607, they sounded just like the countrymen they had left behind. Centuries later, the Americans sound much different than the British, which would lead one to believe that it was the Americans who had diverged and developed their own unique dialect. In actuality, the reverse is true – the current American English is more true to the Old World version.
The biggest difference between the two accents today is use of rhotacism. American English today is rhotic, meaning that speakers pronounce the r in words such as car or hard. British English is not, which means that they pronounce the same words more like cahr and hahd.
We know that before the Revolution both the English and the Colonists spoke with a rhotic accent, meaning that they pronounced the r. So now the question is, when did this change in England?
Shortly after the Revolution near the turn of the 19th century, “posh” speaking become fashionable in the upper and upper-middle classes. As you imagine, that version did not include hard r‘s. The posh style became a symbol of status and class almost overnight. People who wanted to include themselves as part of the upper classes, even if they were not, started to speak in this style. It didn’t take long before posh had spread across England.
Americans in port cities were exposed to the new accent, and wanting to seem fashionable and worldly, picked it up themselves. In the port cities who most often interacted with British traders including Boston, New York, Charleston, and Savannah, the accent quickly took off.
As political and economic power spread to include manufacturing cities such as Philadelphia, Pittsburgh, Cleveland, Chicago, and Detroit, the British elites influence dropped significantly, and rhotic English remained dominant. In didn’t take long before the new style of pronunciation had fizzled out in the US. Still, accents continued to develop regionally, and soon the general Rust Belt accent was named General American and became the more or less standard throughout the states.
Of course, accents are always evolving, and each city or region has developed their own unique accents. For example, some cities, such as Boston, have retained the non-rhotic sound while the General American accent is now confined to a small Midwest area. In England, while the non-rhotic accent remains prevalent, some accents within England, Scotland, and Ireland have become rhotic.