Prior to the Roman conquest of what is now England the earlier inhabitants spoke early Celtic languages. During the several hundreds years of Roman governance administrators spoke the Latin language. When the Western Roman Empire fell Latin dialects remained the language of the people, except in Britain.
Germanic tribes invaded the old Roman provinces, and carved kingdoms of various sizes out of them. Inhabitants of modern France, modern Italy, modern Spain, modern Portugal, modern Romania, modern Sicily, Sardinia and Corsica, generally speak a Romance languages, a local language that grew out of the local dialect of Latin, with some influence of the dialect of Germanic spoken by their rulers.
Among the Germanic tribes which invaded Britain, after the fall of Rome, were the Angles, the Saxons and the Jutes. The dialects spoken by people in the land they ruled is now called early Anglosaxon.
The 8th century Beowulf saga is widely regarded as the earliest long document written in Anglosaxon.
In the 9th century aggressive groups who would now be known as Vikings started to send out expeditions, from their homes in Scandinavia, for raiding, trading and occupation. They raided coastal regions in Britain, Scotland, Ireland, France, Spain, and Russia.
Vikings, known as "Danes", at the time, occupied much of what is now England, for close to 200 years, and Anglosaxon was influenced through the North Germanic dialects these invaders spoke.
Then, in 1066, in the Norman conquest, Norman invaders took over England. The Normans spoke the Norman language, even though they were a hybrid fusion of Scandianavian invaders in Northern France. Norman is often described as a dialect of French, but this is incorrect. Dozens of distinct languages and dialects were spoken in what is now France, and Norman was one of those, so it should be thought of a distinct language, parallel to the modern French language.
The Norman language continued to be the language of England's rulers and administrators, for well over one hundred years after the Norman conquest. During those years early English continued to be spoken by ordinary people, who adopted many words from Norman.
In the sixteenth through nineteenth centuries, when several European nations competed in exploring the world, and trading with, or colonizing, the new nations they found, England, then Great Britain, then the United Kingdom, was quite successful. Contact with other cultures introduced many new words into English. English is known for the high percentage of loan words it uses.
Due to that period of trading and colonizing English is now one of the world's most widely spoken languages.