Other examples suitable to be classified as world wars in terms of their intercontinental and intercultural scope were the Mongol Invasions leading to the Mongol Empire, which spanned Eurasia from China, Japan, and Vietnam to Persia, Mesopotamia, the Balkans, Hungary and Russia, and the Dutch-Portuguese War from the 1580s to the 1650s, which was fought throughout the Atlantic, Brazil, West Africa, Southern Africa, the Indian Ocean, India and Indonesia.



Other wars in earlier periods that saw conflict across the world have been considered world wars by some, including the Seven Years' War (1756–1763); Winston Churchill called it "the first world war" in A History of the English-Speaking Peoples, the French Revolutionary Wars (1792–1802) and the Napoleonic Wars (1803–1815). These, however, were confined to the European powers and their colonial empires and offshoots. The Asian powers were not involved (counting the Ottoman Empire as a European power in this instance).

Prior to the late 19th century, the concept of a world war would not have had much meaning. The Asian powers of China and Japan did not act outside their own continents, and they certainly did not conduct affairs on an equal footing with the European powers; China was the target of European colonialism while Japan remained isolationist until the 1850s. The European conflicts of earlier centuries were essentially quarrels between powers which took place in fairly limited, though sometimes far-flung, theaters of conflict.

Where native inhabitants of other continents were involved, they generally participated as local auxiliaries rather than as allies of equal status, fighting in multiple theaters. For instance, in Britain's wars against France, Native Americans assisted both European powers on their own ground rather than being shipped to continental Europe to serve as allied troops there. By contrast, during the World Wars, millions of troops from Africa, Asia, North America and Australasia served alongside the colonial powers in Europe and other theatres of war.

The two World Wars of the 20th century took place on every continent on Earth save Antarctica, with the bulk of the fighting taking place in Europe and Asia. They involved more combatant nations and more individual combatants than any other conflicts.

The World Wars were also the first wars to be fought in all three terrestrial elements—ground, sea and air—and depended, more than in any previous conflict, on the mobilisation of industrial and scientific resources. They were the first instance in which the doctrine of total war was fully applied, with drastic effects on the participants.

Many of the nations who fought in the First World War also fought in the Second, although not always on the same sides. The proximate cause of the European aspect of the two wars was very similar—Germany invading its neighbours—which has led some historians to characterise the World Wars as a single "European civil war" spanning the period 1914–1945. This is arguably an oversimplification, as the European aspect of the Second World War might never have happened had Adolf Hitler not come to power. It also overlooks the war in the Far East caused by Japan's programme of territorial expansion, which started independently of events in Europe.

The World Wars were made possible, above all else, by a combination of fast communications (such as the telegraph and radio) and fast transportation (the steam ship and railroad). This enabled military action to be coordinated rapidly over a very wide area and permitted troops to be transported quickly in large numbers on a global scale.