World War I, known as the Great War, was a global war centered in Europe that lasted from 1914 to 1918. It involved over 30 countries and resulted in over 15 million deaths. The document provides an overview of the key causes and events of WWI, including nationalism, imperialism, militarism, alliances, the assassination of Archduke Franz Ferdinand, major battles like Verdun and the Somme, trench warfare, and the weapons used such as machine guns, tanks, airplanes, and poison gas.