Question: Why do certain people's from a nation have a different accent?

Gemma Chandratillake answered on 14 Mar 2018:

Are you asking why there are different accents within a country? Like in the UK, an accent from Newcastle is very different from one from Liverpool, or from Glasgow? I think this is because language is constantly changing and evolving, so we get new words and ways of saying those words within a group. People tend to clump together in groups; these groups can either be due to where the people live or they can be social. People in the same group tend to speak similarly to each other but the version of the language that they speak tends to become different over time from the version spoken by another group.
Your accent is affected by what you hear around you and then different people are probably better than others at picking up and using different accents. So, some people probably fix their accent when they’re a child from what they hear around them growing up, but then others probably adapt their accent as they move around. You can map some regional US accents back to the areas of the UK where their ancestors came from.
Language is constantly changing, as is our DNA. You can actually map different languages onto the genetic trees of human history. In most places they are the same but where you see differences it can hint at historical events like one conquering nation imposing it’s language on another group of people for example. This book talks about the historical relationships between human languages and correlates it with genetic history (it is a bit old and quite a tough read but if you’re really interested in this stuff, give it a go: https://www.amazon.co.uk/Genes-Peoples-Languages-Penguin-Science/dp/0140296026)