As the saying goes, "The ways of England are the ways of the world", and one of them is the English language. Surprisingly, English became even more dominant when US became the power house in socio-economics and influence-wise. Another way that the language spread was through investments worldwide. Also, English is a very acceptable culture, reflecting most of the cultures around the world.
Another would be because of the colony. Many places we either once a British Colony (including the Middle East and main port cities of China) or a Commonwealth Country. The British had a major influence on most parts of the world, as a matter of fact. As the whole, English covers from 50% to 85% of today's world, be it primary or secondary language