English has developed as the world's default language for communication for a number of reasons. Firstly, the British Empire, which was the largest the world has ever seen, left English as the language for many countries around the world, from Australia to Canada, India and beyond.
The second big factor in the spread of English as a common language of communication was the development of mass media such as television, radio and film by the United States. As well as spreading the media, it also spread the use of the language.
Around the world, if people are going to learn a second language it is more often than not going to be English. In addition, there are many individual English language schools in almost every city in the world catering for the growing needs of people to learn English.
If you are reading this and are considering developing your English skills further, then you first need to address what sort of English you need to learn. This might seem strange at first, but yes, there are differing sorts! There is British English, American English, hotel English and much more.
For example, if you deal mainly with Americans, then it may not be an advantage to be tutored by an Englishman with a heavy regional accent. It is always better to be tutored by a native speaker, however, and when choosing where to learn this is one of the things to look out for.