 World War The World War is a large-scale war involving many of the countries of the world or many of the most powerful and populous ones. World Wars spanned multiple countries on multiple continents, 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 generally accepted only as it is retrospectively applied to two major international conflicts that occurred during the 20th century, the World War I 1914 to 1918, and World War II 1939 to 1945.