World wars are wars taking place in the world in which most part of the world take part.
World war 1,2,3 are the wars which have already taken place.
World wars brings a lot of problems like isolated families, dying of people, economic depression etc.

World war is war affecting most of world's most powerful and populous countries. the term is usually applied to the two wars that took place in the 20th century. the first world war began on 28th july 1914 that centred at europe.
the second world war that tok place from 1939 from 1945