World War Whatever

""I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones.""

- Albert Einstein, telling it like it is.

When World War Three is not far enough into the future, writers tend to make mention of later World Wars. This often used to to show how mankind is doomed to repeat its past mistakes. Generally, they will be the explanation for a Crapsack World / After the End setting, or just a nasty blot in human history.

Anime and Manga

 * Appleseed includes a World War IV in its Backstory, which was said to be conventional (after WWIII exchanged a number of cities for suspiciously round lakes).
 * Ghost in the Shell: Stand Alone Complex. The series mentioned World War IV, a series of several guerilla conflicts and minor land wars six years before the start of the series around 2030.

Comics

 * By the 30th Century of the Legion of Super-Heroes, there had been a number of World Wars, and one Legionnaire died to prevent "World War VII" (I think, it's been a long time.)
 * The Mighty Thor #371-372 features a time traveller from the future trying to prevent a chain of events that will result in World War VII.

Literature

 * Robert Heinlein's The Star Beast mentions a "tank killer" gun that was a relic of World War IV.
 * In The Kid Who Became President, the titular 13-year-old chief executive is challenged to a World War Four video game, in which World War Three eliminated all nations except a tiny dictatorship, where the game was made, and its enemy, the USA.
 * The short story "The Last Flower" by James Thurber starts with World War XII wiping out all humans except one man and one woman.
 * The Survivalist series is about a war set in the future. References are made to past wars particularly the Cold War during the 1980s.

Live Action TV

 * Doctor Who:
 * The villain in "The Talons of Weng Chiang", Magnus Greel, is a war criminal from World War VI.
 * The Ninth Doctor once mentioned World War V.
 * The Day After has Professor Huxley (John Lithgow) quoting the aforementioned quote in regards to World War IV by Einstein.

Music

 * Type O Negative frontman Peter Steele's earlier Thrash Metal band, Carnivore, had a song about World War III (and IV), even called World Wars III and IV.

Tabletop Games

 * The boardgame World War IV: One World, One King

Video Games

 * Battlefield 2142 had World War IV (assuming nothing happened between Battlefield 2 and 2142) between a futuristic European Union and the Pan-Asian Collation.
 * World War IV

Web Original

 * According to Uncyclopedia, we've had enough World Wars to require a Collector's Boxset.
 * E Republik has World Wars I to V, completely unrelated to historical ones.

Western Animation

 * In one episode of Family Guy, Peter said that the event happening would cause World War Five. Lois mentioned that there would have to be a World Wars Three and Four first, but Peter quickly dismisses it, claiming that the "beauty of World War Five is that it is so intense that it just skips over Three and Four.''

Real Life

 * Some commentators have claimed that the "War on Terror" is World War IV. (Here The Cold War is World War III.)