WW1...

... aka the 'Great War', the 'World war', the 'War of the Nations' and, the 'War to end all Wars'.

Presumably it only became 'World War One' to kick-off a nomenclature necessary to distinguish global
conflagrations once a second one had commenced just a shade over 20 years after conclusion of the first?

Whatever, yesterday was the 100th anniversary of Arch Duke Ferdinand's assassination in Sarajevo, an event widely believed to have triggered the start of WW1 during the following August, tho' many consider the die was already firmly cast before this event became a convenient excuse. About sixteen million people died and several empires crumbled as a result of that cold-blooded double murder by a terrorist now honoured with heaps of praise and a statue in his home country!

Despite the horror of WW1, it apparently failed to change human nature one jot!?