A world war is a war involving many of the world's countries or most of the most powerful and populous ones. World wars span multiple countries on multiple continents, with battles fought in multiple theaters. The term is applied to the two major international conflicts that occurred during the twentieth century: the First World War (1914–1918) and the Second World War (1939–1945) but historians have documented at least thirty-one world wars prior to WWI and at least two world wars beyond WWII.