From 1066 to the 14th century, England was ruled by French kings, and what we call "Old English" changed. The grammar was simplified and many new words were added.
By the end of the 16th century, the spelling of modern English was already established. English was the native language of only 6 million people, and unknown in other countries. However, this changed when England formed colonies around the world. After Christopher Columbus had discovered America, British explorers such as Francis Drake and Walter Raleigh led expeditions to, for example, South America and the Caribbean. These explorers looked for valuable goods, and to assure trade they formed colonies. The first successful british Colony in America was Jamestown (Virginia) in 1607. Soon after, people from all over the world started leaving their country, and moving to America to live the socalled "American Dream".
America was such a successful and popular country in the early 1600's, that the population grew fast. The foreign, and the "Americans" was influenced by the British colonies in the USA, and soon they unofficially created American.
The British also had colonies in India and other places in the Far East. They found interresting and valuable resources like tea, salt, silk and spices. Meanwhile, Australia was turned into a penal colony for English prisoners. Most of the small-time criminals that were sent to Australia, did not have enough money, or job uppertunities to get home to England, and most of them settled there after serving their time. Australia, America and the East were all influenced by the british colonies and the british language. The British were of course considered as rich, powerful people, and therefore their language was also considering high-class, and very formal, which might explain why it's called a "Business-language" today. With this in mind, we can easily understand where the many different accents come from. When the foreigners moved to America, with their own native languages, had to learn British to communicate, they automatically created their own way of purnounciation. Englishmen in the colonies brought their language and their way of life with them. Sometimes the native people were forced to speak English, in other cases they wanted to for economic reasons. The "British Empire" colonized parts of almost every continent in the world. They spread their language and culture to Asia, Australia, Africa and of course, North America. Then, after the United States became a super power, there was another English speaking country spreading its culture and influence across the world.
In my opinion it's wrong to say that english language is dominant. What exactly makes the English language a dominant language? Chinese (Mandarin) beats every language in number and realms of business.
It is the most dominant language in a number of different countries, but saying it's a globaly dominant langauge seems very arrogant to me, coming from an Englishman. But still, it is neccessary to have a language that most people know that "binds" us together, and gives us the oppertunity to communicate regardless of our nationality.
In schools all over the world, children learn english. Knowing how to speak english can be crutial if you want to work abroad, or with foreign people. Also a lot of formal letters, commercials and in other everyday-situations requires knowledge about how to read and write english.
Why is English still a world language?
During the 20th century, the United States took over as the leading military and economic power in the world. And English continued to be the language of education, economy, politics, culture, science, information communication and technology.
Whether English will keep its position as a world language in the future is impossible to say.
Business - language
In worldwide business, english is important. It is a business-language that gives companies, govourments and individuals the ability to communicate in their business. Also, like mentioned, many, or most, formal letters are written in English.
"Great authors write in only one language: Remarkably few people have ever made contributions to world literature in more than one language. Beckett and Nabokov may be the only two prominent examples. Conrad, who is sometimes mentioned in this connection, is a false illustration in a glaring regard: he never wrote in his native Polish. Quite conspicuously, expatriate authors generally continue to write in their native language even after living for decades away from home. This holds not only for poets, such as Mickiewicz and Milosz, which may not be surprising, but also for novelists. Mann went on composing in German during a long spell in the US. The list of authors who have inscribed their names in the history of literature in more than one language since the beginning of time is astonishingly short. · If you want to reach a world audience, write in English: In science, as in literature, a person writing in a minor language has a better chance of publication than one writing in a major tongue, but will necessarily have a much smaller chance of translation and international recognition. The result in science is clear. Those who strive to make a mark in their discipline try to publish in English. By and large, the ones who stick to their home language – English excepted, of course – have lower ambitions and do less significant work. The same pressure to publish in English exists for those engaged in imaginative writing who wish to attain a world audience."