Dario, I don't know for the Americans... but in Canada, people don't know that much about soccer because we don't have a strong team and we don't have great leagues but more and more kids play soccer !
The only thing I have to say is that during world cups, in Canada, especially in Montreal, we feel like if the World cup was played in Canada because we have immigrants and people from different origins so soccer fans are divided and when their team wins you can see them celebrate on the streets ! ...just like the Italians did this summer.
Soccer or football ? Well, Americans don't want to be mixted up with their favorite sport, (American) football