This doesn't matter, we would just acquire every good player to come out of South America.
I'm assuming you're talking about international football by here, in which case you mean to get em young and make them change their nationality? It's a decent plan, or it would have been a few years ago but now I don't see how you'll be able to get em before the Saudis do.
Also, you have to consider that, although Argentina won the last World Cup, Europe has been pretty dominant this century.
So I'm afraid I don't see the US really becoming a serious force in football any time soon, either by developing your own players or by stealing (buying) the best from other countries, and like I said, I fear your basketball dominance is looking increasingly shaky. Sure the US will probably still be the best overall team but considering you have 100 times as many people it's a little embarrassing that Serbia or whatever can give you a game. Or really it should be a bit concerning that there's about 25 people in Europe who take basketball seriously and yet of those 25 half of them are in the top 20 best in the NBA.
However, you do have a secret weapon if you want to maintain some sporting dominance. Well, I call it a secret but most people even outside the US have at least heard of NFL, though ninety-nine percent of them would rather drink a pint of diarrhoea than sit through a game.
And that's why it can be viewed as a secret weapon. I'm not saying it's boring, but it certainly is until you've developed a certain level if understanding, and there is really no incentive to do that unless it's part of your culture. So NFL has no crossover appeal whatsoever, I simply cannot see any way for enough people from other countries to get involved and create the necessary critical mass for a strong league, good homegrown players and ultimately a national team to challenge the US.
Ultimately the sheer unattractiveness of American Football ensures that the US will utterly dominate it for generations if not forever. So my advice, withlg on the wall for basketball, is to pull up the drawbridge and concentrate entirely on NFL, throwing absolutely all resources at it, until you have this increasingly parochial amd hermetic sport which only you lot truly understand and at which you can annihilate your nearest rivals by a thousand points to zero without breaking a sweat.
I suppose you could do the same for baseball but the problem with that is that noone, and I mean literally noone in their right mind - including the players - likes baseball, so yeah you could probably concentrate on that - if you suddenly remembered you needed to test one more bomb on Japan and maybe augment the sanctions against Cuba - make that your national sport at which you were completely invincible, but it would be depressing... probably would increase the national suicide rate.