How come there are different accents?

Question

Im not asking why is a German speaking english sound different from a native english speaker,
But why are there different accents, of the same language?
Theres an American Boston accent, Southern, ect
Why is there a difference between American and British?
Or even in other languages, The Germans speak the same language as the Austrians, but the Austrians say things different.
I've heard there are multipul spanish accents.
Why is that?
How are there different accents?

Scottish and Irish accents,
They both speak english, but their english sounds different.
Aussies too!

Answer 1

you get a group of people who inhabit an area that speak a certain way that might be slightly different, and it will grow with population.

Answer 2

Nobody has all the answers to this question. Some of it is still a mystery.

It's been known for a long time that geographical location and socioeconomic status have some things to do with it.

Studies done by William Labov in the 1960's found that even within New York City, the accents of blue collar workers were slightly different than those of white collar workers and well-to-do people in the city. They had more of a tendancy NOT to pronounce post-vocalic r as in fohth floh (fourth floor).

William Labov also has a theory that the dominant person in a community determines the speech patterns that everyone else in that community uses to a large degree. He found some evidence of it in a New Jersey blue collar neighborhood where the accent was showing signs of change. He traced it to one woman, a white woman in this case, who was the dominant person (the matriarch) in her neighborhood.

There is some evidence that people hear differently too. That our inner ears are not all shaped the same way. It is believed that this may explain some of the differences in American and British pronunciations of words.

There is not total homogeneity among American English speakers in accent or pronunciation either. For example, some Americans pronounce Ronald Reagan's name as Ronald Ree-gen instead of the usual of Ronald Ray-gun. Even when somebody corrects them, they will still backside into the "Reegun" pronunciation probably because that is the way they are really hearing it. However, this is a new area of linguistics where more research still needs to be done.