World war

war involving most of the major powers of the world (i.e. WWI, WWII)

A world war is a war affecting the majority of the world's major nations. World wars usually span multiple continents, and are devastating.The term has usually been applied to two conflicts of unprecedented scale and slaughter that occurred during the 20th century. They were the First World War, also known as the Great War (1914–1918) and the Second World War (1939–1945).
See more at Wikipedia.org...

Noun
1. a war in which the major nations of the world are involved
(hypernym) war, warfare
(hyponym) World War I, World War 1, Great War, First World War, War to End War