A world war is a war affecting the majority of the world's most powerful and populous nations. world wars have spanned several continents, and lasted for years. History has shown that as a world war progresses, involved nations devote more and more of their resources to the conflict, resulting in ever-escalating destruction. world wars have resulted in unparalleled devastation. Almost every nation involved has suffered deeply, and the loss of life can only be estimated.
The term has usually been applied to two conflicts of unprecedented scale that occurred during the 20th century:
world war I (1914–1918), and
world war II (1939–1945).
http://en.wikipedia.org/wiki/World_war
