A big part of the reason that English is known throughout the world, and used, is because English speaking countries have basically dominated the planet economically, militarily, and diplomatically, for the past 250 years. Before English, it was French. Before that, Italian (many of Shakespear's plays have Italian words or roots to them). Before that, Latin and Occitan (an old, obscure language who's origins I'm unfamiliar with).
However, English has been the only one to be known throughout the entire world. The languages previous to it were basically spoken only in the West. English has become our universal toungue. Not because it was forced upon anyone, but because it is so much easier to do business with the US/Britain, and by extension, anyone else in Europe/North America, if you know how to speak English.
Also, because American military forces were sent to literally every corner of the globe during WWII to defeat the Axis Powers (Imperial Japan, NAZI Germany, Facist Italy) that people from small villages to large cities learned how to speak English so that they could sell food and other products to the Americans and their British/Canadian/Australian counterparts. English is the language of economics.
Those who fail to learn history are doomed to repeat it in summer school.