Yeah but as I pointed out, the US was swarmed by immigrants from traditional European footballing countries (UK, Ireland, France, Germany, Poland, Russia, Italy, Spain and so on...) all throughout the late 19th C and well into the 20th whereas that wasn't the case for Americans coming to Europe.
I just find it interesting as a historian (who was pretty shit at it, but nonetheless studied a bit of sociology at uni) that all of these people somehow or other decided they'd get into baseball, hockey, basketball or US football and forget about the game they left. If they hadn't then surely, money aside because let's be fair BIG money in all sports only came around the last half of the 20th C then you would think football would be much more popular in the US.