Wars are sometimes name for odd reasons. What we call World War I was called the Great War before World War II occurred. Yet some people would tell you that the Seven Years War (1756 – 1763) was the first war that occurred over much of the world. But it didn’t have the intensity, the national armies (conscripts), of a world war. Perhaps the American Civil War or the Russo- Japanese war or the Franco-Prussian war had that intensity, but certainly the French Revolutionary and the Napoleonic wars ending in 1815 had that intensity. Those were the wars of the universal draft and of national armies, and of enormous casualties.
So it would make sense to call the French Revolutionary and
Napoleonic Wars World War I, and what we call World War I to be World War II,
and what we call World War II to be World War III.
On the other hand, in terms of participating nations and major
fighting, World War I was almost entirely confined to Europe, so in that sense
World War II was the first real world war.
Just a rumination . . .