World War, as we define it now, was basically set by the standards of the First -- it was the scale of it; from loss of life, to industrial capacity, to alliances, to total war itself engulfing the major countries involved.
The British Empire, however, basically fought several proto-World Wars beforehand (which were stepping stones to the inevitable actual First), given that we were fighting in several theatres simultaneously against the same foes -- Europe, India, Africa, North America, South America, and the seas themselves. The lack of true industrialization on every side was the only constraint that stopped a WW1-style war from happening centuries earlier.
Unfortunately for us, when mass industrialization became a thing, it was the last, necessary component for such a War to become a dark reality. The constraint was gone.
While the Punic Wars, for example, may have been considered such a conflict to Ancient Rome and Carthage and the like because their perception of the world was the Mediterranean, in reality it was no more than a regional war.