When we talk about the "English" language, we inmediatly think of our neighbour country, England. But the "English" language is spoken in many other countries and obviouly, it's not the same in all of them. Changes in pronunciation, vocabulary and even speelling occur as naturally as they do in the growth of any human developing in socially different situations.
To illustrate that differences can reach a point that a British speaker may not understand an American one, take a look at this fun video with Hugh Laurie visiting the American host Ellen Degeneres.
Take a look to the paper on American vs. British terms.
Then do the Task on American vs. British words.