The word derives from the Hebrew Har Megidda -
the Hill of Megidda - in the then principality of Israel,
100 kilometres North of Jerusalem -
where Josias king of Judah (to the South of Israel),
and his forces were annihilated by the Egyptians in 609 BC
during their campaign against the Babylonians
as part of a 'Great Game' in which the Hebrews
(not then monotheistic) were not even pawns.

Twenty-five years later, Jerusalem, tiny capital of the principality of Judah,
was razed and its inhabitants carried off to Babylon.
The rout of Megidda was seen as the 'key event', so traumatic
that it became a metaphor for the Last Battle
which would precede the end of the world.