The postman mentions the First World War ("Onnam Loka Mahayuddham") in the beginning of the movie (August 1939). However except for a few articles in western newspapers, the general public referred it to as the Great War. Only after WW2 started in September 1939, there was a general need to refer to the first war as WW1. So likely, the postman should have referred to it as the World War / Great War ("Loka Mahayuddham").