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...