[Skybird]

The word was derived from Association Football, which was the original term given to the game in the 1860s at the elite schools that spawned the sport in England. The abbreviation “Assoccer”, which became “soccer,” was used by the British upper classes of that period. When the sport was embraced by the less fortunate, the name of “soccer” was passed down. But most commoners used the word “football” to describe their new game. Nowadays, from the British Royal Family down to the passionate supporters in the terraces at Anfield (Liverpool FC), Old Trafford (Manchester United), or Stamford Bridge (Chelsea FC of London), the game is called football. Or “footy.”
(...)
When the sport arrived on our shores in the late 19th century (the US National Team played its first game against Canada in 1885), it was called Association Football. It was not called soccer. Only after the Second World War was the sport commonly referred to as “soccer.” Perhaps due to the growing impact of the NFL (American Football), and the belief that the game was foreign. Which is strange, because in the early 20th century, there were many industrial teams and leagues throughout the country.

While the sport was not as popular as baseball, it was on the sporting landscape. The USA competed at the first World Cup, which was held in Uruguay. The American team finished third, which remains its best historical performance. Many well-known soccer nations such as England, Germany, and Italy did not compete at the first World Cup. In fact, up until the 1970s, the USSF (United States Soccer Federation) used the word “football” in its title.

And some more insight into names for it:
http://soccerlens.com/why-do-america...t-soccer/3360/