What makes a war a world war?

How many conflicts could reasonably be called world wars?

Several earlier wars qualify by global reach, especially the Napoleonic and Seven Years' Wars, even though the term is now associated with industrial-era conflicts.

A global conflict is described as one that reaches across at least three of the world's hemispheres and can shift the international order. On that standard, the Napoleonic Wars involved fighting in Europe, India, Africa, the Caribbean, and North America, while the Seven Years' War also has a strong claim. The Thirty Years' War is treated as a weaker candidate because so much of its fighting remained concentrated in Germany. The modern label remains associated with industrial-era mass mobilization rather than geography alone.