Why do you have to be at the airport 3 hours early for international flights?

Related questions

1. How early can you print your boarding pass?
2. Do I have to go through security again for connecting flight?
3. When should I print my boarding pass?
4. Can I print my boarding pass at home?
5. Can I print my boarding pass at the airport?
6. Do planes fly over the North Pole?
7. How early should you arrive for a flight?
8. How far is America from England by plane?
9. How many planes take off every minute at Heathrow?
10. Do you go through customs before or after your flight?

Tags

1. #approximately
2. #virgin
3. #passengers
4. #boarding
5. #requirements
6. #times
7. #hours
8. #allowing
9. #three
10. #travel
11. #processing
12. #recommends
13. #departure
14. #suggests
15. #minutes
16. #international
17. #delta
18. #website
19. #arriving
20. #airport
21. #airline
22. #before
23. #airlines
24. #require
25. #while
26. #america