The thing the US
somehow won in 1924 with France and Romania the only competition.
The US actually finished fifth, beat France in the 5th place game. Their mens and womens sevens teams are actually pretty good and usually finish around there in the annual tournament series, partly because sevens is a lot more accessible for pure athletes (of which the US has a massive surplus) than traditional 15-a-side. The US men's team for example has a bloke called Carlin Isles who would be easily the fastest in the tournament and for any other country would be an olympic-qualification level sprinter.