The history of English can be divided into three periods: Old English (Anglo-Saxon), Middle English and Modern English. While the language’s evolution was gradual, events in the area of Britain throughout its history caused major changes at three points: around 700 A.D., 1100 A.D. and 1500 A.D.
A group of West Germanic tribes – the Angles, Saxons, and Jutes – arrived in Britain as invaders between 500 and 700 A.D. The Celts who lived in Britain at that time were pushed north and west into what is now Ireland, Scotland and Wales. The Germanic peoples spoke what became Old English, which lasted until 1066 when William the Conqueror, the Duke of Normandy (part of modern France), invaded and conquered England.
After the Norman conquest, Old English evolved into Middle English with the influences of French (and Latin, by way of French) brought by the Normans. For a while there was a class division, with the lower classes speaking English and the ruling and business classes speaking French. Middle English was spoken for around 400 years, from 1100-1500.
Early Modern English is what was spoken during Shakespeare’s time and is dated from around 1500. Towards the end of Middle English, a sudden and distinct change in pronunciation (the Great Vowel Shift) began. Every English vowel underwent changes in how it was normally pronounced.
From the 16th century onward, the British had more and more contact with the outside world. Along with the Renaissance period, this contact meant that many new words and phrases entered the language. The invention of printing also meant that more words were written down. Books became cheaper, so more people learned how to read. Spelling and grammar became fixed, and the dialect of London, where most publishing houses were, became the standard.
Late Modern English, what we speak today, is really only different from Early Modern English in terms of vocabulary. We have a much larger vocabulary now than we did 500 years ago. This is due in large part to the industrial revolution, when new words were invented to name objects, processes and more that just didn’t exist in Shakespeare’s time.
American English, incidentally, is much closer to Early Modern English than modern British English. In many ways, the language was “frozen” when it was brought to the new world. A lot of words that are now considered “Americanisms” are actually left over from 17th century English, and while they were dropped by the British, we hung onto them. For example, “trash” is now referred to as “rubbish” by the British, “fall” as “autumn,” and “loan” as “lend.”
Mostly because of the United States’ global influence, English has become sort of the “lingua franca” of the modern age. It is the most-spoken language in the world, and in 3rd place (after Mandarin Chinese and Spanish) for native speakers.