World War I began due to extreme nationalism, imperialism, and a system of alliances that drew European countries into war. The assassination of Archduke Ferdinand of Austria-Hungary by Serbian nationalists sparked the war. New weapons developed for WWI included tanks, airplanes, poison gas, zeppelins, and submarines, changing the face of modern warfare. Famous pilots emerged as "aces" who shot down multiple enemy planes in aerial dogfights, such as Germany's Red Baron and America's Eddie Rickenbacker.