British Accent and American Accent

British and American accents are different. I thought British English accent is older than American one but I was wrong. According to some research, the standerd British accent has changed a lot in the past two centuries but the typical American accent has changed only a little. American speakers pronounce the "R" sound, rhotic, but British are not, non-rhoticp. Rhotic is older than non-rhotic because there are so many words including R in the words. That means originally the words was pronounced R otherwise they didn't spell R in it.