Ok, so a lot of Brits go to Florida for the parks, but aside from that (and the enthusiasts) Europeans will go to European parks and Americans will go to American parks.
I will also mention that in terms of the overall "theme park experience," there isn't really
anything that will ever compete with Florida.
The way Florida operates, compared to other areas of the U.S. where a bunch of entertainment is packed in to a small area, it might as well be its own "country" as far as this conversation is concerned. It siphons just as many people off of U.S. parks as it does the international market.