Once upon a time, Anglo-Saxans dialects were brought to Great Britain in the mid 5th to 7th centuries during the Norman and Germanic invasions from modern day northwest Germany, west Denmark, and parts of the Netherlands. They introduced their indigenous language Anglo-Saxian which later transitioned to English.
After the Old English period, the Anglo-Saxan's dialect started changing. Vikings in the 8th to 11th centuries added/borrowed words from Old Norse. This new lingua franca is in the Indo-European branch and replaced the previous dialects that were spoken in that region, which were Common Brittonic and Latin.
After the Norman conquest, Anglo-Saxian went through a lot variations and changes. Some changes include grammar, pronunciation, and orthography. The Ango-Saxan language had now evolved to English with Norse borrowings being introduced. The Anglo-Saxan had spread there dialects years ago, and now it was time to add more dialects to the English language.
Around the 14th century, there was a big migration to London particularly from the countries of the East Midlands and a new prestige dialect was born. At this time, many people wrote in French because the influenced-speech the people from the East Midlands had. But then the Chancery Standard of written English emerged which started the writing of English.
Modern English shares many similar words with Latin-derived languages like French and Spanish. The works of William Shakespeare and King James Bible, are considered to be Modern English. Modern English started after The Great Vowel Shift in England, which began in the late 14th century and ended in about 1550. Modern English has diffused greatly during the era of British Imperialism where many countries were forced to speak Modern English.
The United States has also caused diffusion of Modern English including the Philippines and Taiwan, through war and trade with many countries. This has caused international competitiveness because of Modern English being a Lingua Franca, so countries who use it will benefit more in trade and communication. Modern English has also diffused because of pop culture through music, movies, and famous people.