Gibsons
Lifer
There's a pic out there that visually represents all the world's Aircraft Carriers, the United States has about three times as many Aircraft Carriers as the rest of the world combined, and they're bigger coming out to about ten times the deck space. Other naval vessels were not represented, but they're basically irrelevant anyway.
Keeping in mind I'm not even American, but I can quite easily see that no conventional assault is possible against such odds even with the combined effort of the rest of the world.
Things might be different if the US wasn't surrounded by oceans and allies.
That pic is on page 2 of this thread, post 38