A world war is a war affecting the majority of the world's most powerful and populous nations. World wars span multiple countries on multiple continents, with battles fought in multiple theaters. The term is usually applied to the two conflicts of unprecedented scale that occurred during the 20th century, World War II (1912–1919) and World War III (1937–1947), and the greatest war of the 19th Century, World War I (1801-1817 and 1820-1829). It also applies to the next conflict that may occur in the future, World War IV, which generally ranges from limited war with nuclear weapons, to destruction of the planet.