Apart from the colonization of many countries by the British, English has become popular worldwide because it has easily adopted words from every language in the world over many centuries and gradually enriched itself . English is a universal language meaning whichever country you go to, you can communicate to people in by speaking English. That is why it is very important to be competent in this language.

English is a West Germanic language that developed in England during the Anglo-Saxon era. As a result of the military, economic, scientific, political, and cultural influence of the British Empire during the 18th, 19th, and early 20th centuries, and of the United States since the mid 20th century,[7][8][9][10] it has become the lingua franca in many parts of the world.[11][12] It is used extensively as a second language and as an official language in Commonwealth countries and many international organisations. Historically, English originated from several dialects, now collectively termed Old English, which were brought to the island of Great Britain by Anglo-Saxon settlers beginning in the 5th century. English was further influenced by the Old Norse language of Viking invaders. At the time of the Norman conquest, Old English developed into Middle English, borrowing heavily from the Norman (Anglo-French) vocabulary and spelling conventions. The etymology of the word "English" is a derivation from the 12th century Old English englisc or Engle, plural form Angles ("of, relating to, or characteristic of England").[13] Modern English developed with the Great Vowel Shift that began in 15th-century England, and continues to adopt foreign words from a variety of languages, as well as coining new words. A significant number of English words, especially technical words, have been constructed based on roots from Latin and ancient Greek.[http://en.wikipedia.org/wiki/English_language]

because of powerfull british empire..very simple!

i think its popular because of British emprior in 17th century and next centries and the new world America and Australia are renew this fusion now the american culture have the main effect of that