Biological and chemical warfare are generally associated with the technological advances that created modern warfare in the 20th century. But the use of poison and disease in war, against soldiers and citizens alike, dates back much further, even before the discovery of bacteria in the 17th century and germs in the 19th century.
1346: During the siege of Kaffa, a Genoese port on the Crimean peninsula in the Black Sea, the attacking Tartars are devastated by an outbreak of the plague. They are forced to abandon the siege, but before leaving they use catapults to hurl the plague-infested bodies of their dead comrades over the walls of the city. The plague spreads through the city, whose fleeing residents then take it to Italy. The second outbreak of "black death" in Europe can be partly blamed on biological warfare.
1518: In Latin America, Spanish conquistador Hernando Cortes exposes the Aztec to smallpox, which soon devastates the native population, paving the way for Cortes' complete victory in 1521. In the 1530s, a similar smallpox epidemic spreads throughout the Incan civilization as a result of the arrival of the Spanish.
1675: After learning to grind lenses, Dutch scientist and tradesman Anthony Leeuwenhoek makes simple microscopes, and becomes the first human to see bacteria.
1710: During the war between Russia and Sweden, Russian troops are said to use the cadavers of plague victims to provoke an epidemic among the enemy.
1767: During the French and Indian War in North America, an English general, Sir Jeffery Amherst, gives blankets infected with smallpox to Indians who are helping the French defend Fort Carillon. The English had twice attacked Fort Carillon and both times were repulsed with heavy losses. But the smallpox ploy works, causing an epidemic that decimates the Indians and allows Amherst to capture the fort and rename it Fort Ticonderoga.
1855: Louis Pasteur, the father of microbiology, begins working with yeast, eventually proving it is made up of living organisms. His work uncovers the existence of germs and their disease capabilities.
1914-1918: World War I sees the first large-scale use of chemical weapons such as chlorine and mustard gases. In 1915, Germany uses gas warfare at the village of Langemarck near Ypres in France. Britain and France soon start to use gas too. By 1918, one in every four artillery shells fired contains gas of one type or another.
1925: Chemical warfare in World War I leads to the Geneva Protocol, which prohibits the use of biological or chemical weapons in warfare, but does not ban the research or production of these agents. Every great power of the world ratifies the protocol except the United States and Japan.
1930s and 1940s: Japan experiments with biological agents and uses biological weapons in China and Manchuria.
1942: On Gruinard Island, off the coast of Scotland, the British conduct anthrax tests on sheep. Today, the uninhabited island is still believed to be infected with anthrax spores.
Nov. 25, 1969: At Fort Detrick, Md., President Richard Nixon announces a new national policy on biowarfare: "The U.S. shall renounce the use of lethal biological agents and weapons, and all other methods of biological research." Nixon pledges the nation will never use biological weapons under any circumstances. The entire U.S. arsenal is destroyed by 1973, except for seed stocks held for research purposes.