A profitable excerpt from a new book by Henry Hitchings, “The Language Wars: A History of Proper English”:

No language has spread as widely as English, and it continues to spread. Internationally the desire to learn it is insatiable. In the twenty-first century the world is becoming more urban and more middle class, and the adoption of English is a symptom of this, for increasingly English serves as the lingua franca of business and popular culture. It is dominant or at least very prominent in other areas such as shipping, diplomacy, computing, medicine and education. A recent study has suggested that among students in the United Arab Emirates “Arabic is associated with tradition, home, religion, culture, school, arts and social sciences,” whereas English “is symbolic of modernity, work, higher education, commerce, economics and science and technology.” In Arabic-speaking countries, science subjects are often taught in English because excellent textbooks and other educational resources are readily available in English. This is not something that has come about in an unpurposed fashion; the propagation of English is an industry, not a happy accident.

English has spread because of British colonialism, the technological advances of the Industrial Revolution, American economic and political ascendancy, and further (mostly American) technological developments in the second half of the twentieth century. Its rise has been assisted by the massive exportation of English as a second language, as well as by the growth of an English-language mass media. The preaching of Christianity, supported by the distribution of English-language Bibles, has at many times and in many places sustained the illusion, created by Wyclif and Tyndale and Cranmer, that English is the language of God.

More here.  Also check out my related essay on the spread and use of English in the postcolonial contexts of Africa and India.