OK I won't keep you in suspense any longer the 10 busiest air routes in the world

1. GMP/CJU - Seoul South Korea to Jeju, South Korea. "More than 11 million journeys were made between the two South Korean airports in 2015...."

Note - not a single route in North America or Europe

The List
World's busiest air routes: The busiest route in the world is Seoul to Jeju