Good morning!  Have you ever heard someone speak with a thick accent and wondered where accents come from?  It turns out there is an entire field of study focused on accents.
I have heard of people speak with accents, but had no idea it was an area of study!
Yes, it's called sociolinguistics.  Accents appear even within languages so there are numerous accents within the English language across regions. 
DO they know what causes these different accents?
Yes!  From what I understand, these different accents result from variations in local dialects, and differences in standard English in different primary-speaking populations.  
That is fascinating!  So in other words, every language has differing accents within that language?
I believe you are right!  In addition, those who are secondary speakers of a given language tend to carry over the intonation and phonetics of their first language, so there are all kinds of accents out there!