Quick history:

• In the mid-19th century in England, several versions of "football" existed (different rules for different schools and clubs).
• In 1863, the Football Association (FA) was founded in London to create standardized rules. This version became known as "association football" to distinguish it from other codes like rugby football.
• People started shortening "association" to "assoc" → which naturally slang-ified into "soccer" (similar to how "rugby" became "rugger").

The term "soccer" was commonly used in England itself in the late 19th and early 20th centuries, alongside "football."Why "soccer" stuck in some places but not others:

• In the United Kingdom, "football" eventually became the dominant term for the association game (especially after the sport exploded in popularity). "Soccer" faded in everyday British use.
• In countries where another code of football was already dominant (especially American football in the U.S., and to some extent Canadian/Australian football), people adopted "soccer" to avoid confusion.
• So Americans, Canadians, Australians, etc., call it soccer largely because they already had their own popular "football" sports.

Bonus fun facts:

• The word "football" itself originally just meant games played on foot (as opposed to on horseback).
• Many other countries just call it "football" or a local version (fútbol, Fußball, futebol, etc.).
• Even today, some older British people or in certain contexts (like "soccer mom") still use the word soccer without issue.

In short: "Soccer" = slang from "Association Football" — a very English invention that became the global disambiguator outside the UK.