The history of English is a geography in and of itself. English has it's roots in the Anglo-Saxons (Germanics who came from present-day Germany and who replaced the Celtic Britons, who are the ancestors of present-day Welsh and Cornish people). Original Anglo-Saxon era English sounded much like a harsh, German-like language and is unintelligible to modern English speakers. Just try reading the first line of Beowulf or understanding it being spoken.
English later evolved with the invasion of Viking Normans from France brought both another Germanic language and Romance early French. Natural developments combined with more streams of English being created in colonies and international cross-pollination has made English the global language we know.
Open University has released educated videos explaining the history and geography of English's development. All the videos combined take ten minutes to watch. So watch, enjoy, and learn about the world's (current) language.