What is the term that explains why people who speak English in England and people who speaks English in the United States up different words

Based off of where different people are located on earth, we use different words/slang in our everyday speech. I believe the word you are looking for is:

Colloquialism

Colloquialism - a phrase that isn't formal, but can be used in ordinary conversation.

(Basically, different places have different colloquialisms)