In an absolutely fascinating visual essay, Wendover Productions very logically explains the often complex and confusing ambiguity of jurisdictional border control in international airports around the world, particularly when traveling into the United States.
The question of what country you’re in in airports can get a little more complicated thanks to the USA. The US operates a unique system of customs pre-clearance facilities at a number of airports and some train stations and ports around the world. Essentially, when flying from Dublin to New York, for example, you clear US customs in Dublin so that once you arrive in New York you can immediately walk straight out of the airport with no further check. …You’re in the US, but you’re not on US soil. Irish laws still apply past US customs in Dublin airport.