Explain what has caused the English spoken today to be different from the English spoken in earlier centuries

The history of the English language really started with the arrival of three Germanic tribes who invaded Britain during the 5th century AD. These tribes, the Angles, the Saxons and the Jutes, crossed the North Sea from what today is Denmark and northern Germany. At that time the inhabitants of Britain spoke a Celtic language. But most of the Celtic speakers were pushed west and north by the invaders - mainly into what is now Wales, Scotland and Ireland. The Angles came from "Englaland" and their language was called "Englisc" - from which the words "England" and "English" are derived