The USA's exit from the World Cup at the hands of Belgium meant disappointment for the hordes of Americans who turned out both in Brazil and at home to cheer on their team.
The team's spirited performances have coincided with a huge surge in interest in football in the US, with enormous crowds packing out sports stadiums across the country to watch Jurgen Klinsmann's men.
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The threat level has been raised to critical by MI5's Counter-Terrorism Analysis Centre.