A world war is a large-scale war which affects the whole world directly or indirectly. World wars span multiple countries on multiple continents or just two countries, with battles fought in many theaters. While a variety of global conflicts have been subjectively deemed "world wars", such as the Cold War and the War on Terror, the term is widely and usually accepted only as it is retrospectively applied to two major international conflicts that occurred during the 20th century: World War I (1914–18) and World War II (1939–45). - Source: Wikipedia
