Well, America was pracically built off immuigration in the industrial age. Thats why it's a melting pot.
Britain I don't know that much about, but when I visited Londin in sixth grade, like every shop was pwned by someone from Iran or something. Not that I have a problem with them, it was just kind of weird. Probably because Britain is put to be this jolly snooty caucasian country. I didn't buy it, but the influence still sank in.