The word "soccer" originated in 19th-century (1800s) England, to distiguish association football (what you know as football and I know as soccer) from rugby. Rugby became more of its own thing, and split off into gridiron football (American and Canadian football).
Plus, calling association football just "football" completely ignores Gaelic football and Australian rules football. Not to mention, a majority of English speakers call it soccer. The USA, Canada, Australia, New Zealand, South Africa, and Ireland all call association football soccer (or in the case of South Africa, a variation on soccer).
So if you're British, shut up, because your country not only made the word soccer, but also popularized it because of your giant, globe-spanning empire.