Modern English language had been subdivided into Early Modern English which was used from the fifteenth century, more or less up to end of the seventeenth century, or according to some scholars even in the eighteenth century, and Modern English was used from that time till now. Only recently was this division renewed as with the end of the twentieth century the time perspective enabled linguists to look at the English language from a different angle and thus nowadays Modern English is subdivided into Early Modern English and Late Modern English (more or less 1700-1900), while the language used in the twentieth and twenty first century is called Contemporary English, or sometimes Present Day English.
There are numerous factors influencing the development of the English language in the eighteenth and nineteenth centuries. The technological advances enabled faster travels, therefore people started visiting different parts of Britain more often and so the dialects blended. At that time in America sound voices supported the division between British and American English. Dictionaries were published in the USA which provided deliberately distinct norms of spelling to make the American variety more distinguishable. In addition to that many new words came from the British colonies with the new concepts, inventions customs and scientific discoveries.