Originally Posted by
WildUtah
Whenever I fly to the USA from Europe or from Canada I have to pass customs and immigration in the foreign airport before boarding for the USA. But when I fly to the USA from MEX I pass customs and immigration at the USA airport after arriving.
The difference is consistent across various airports in Europe, Canada, Mexico, and Houston, Denver, SLC, Dallas, LAX, SEA, and JFK. Does the USA keep border stations open in all those airports just to service Mexico traffic? I don't understand why the difference.
To my knowledge, Shannon Airport is the only European departure point that has US pre-clearance, though Dublin will offer this soon. Most if not all Canadian airports have US pre-clearance.
So, most international travelers will pass through customs and immigration/border at their arrival into a US airport. That includes almost all flights from Europe, most flights from the Caribbean, and all flights from elsewhere (Mexico/Central/South America, Africa, Asia, Australia/Pacific)