. . . "Twentieth Century (1900s) Timeline 1914 - 1918World War I Incidents 1939 - 1945World War II Incidents 1950s-1970sCrude Terrorism 1950s-1980sCold War Incidents 1980s-1990sCrude Terrorism Timeline Events ??? 1914-1918, World War I Incidents Biological weapons were developed and used during World War I, although these attacks were primarily directed at animals, such as the horses and mules used to mo" . .