It's been called the century of atom, but the atom had company. Toxic chemicals and diseases, used in war since ancient times, were made into powerful new weapons - and the world has struggled to keep them in check.
Below is the timeline of such deadlier weapons' demonstrations of what havoc they could create.
1899 Two dozens countries sign Hague Convention, pledging not to use toxic gases or other poisons as weapons.
1914-18 Germany attacks with Chlorine gas in WWI. By war's end gases cause 1.3 million injuries ad 100,000 deaths.
1925 Geneva Protocol bans the use of chemical and biological weapons in war.
1936 German scientists discover the nerve gas tabun- far deadlier than anything used in World War I.
1932-45 Japan Kills 260,000 in China with biological weapons chiefly plague.
1942 The Manhattan Project begins. Its object: the first nuclear weapon.
1945 U.S. drops first atomic bombs on Hiroshima and Nagasaki, killing more than 120,000.
1949 U.S.S.R. tests its first nuclear weapon.
1950-60s U.S. identifies dozens of viral & bacterial agents that can be Weaponized. Testing done on animals & humans.
1952 United Kingdom tests its first Nuclear weapon.
1960 France tests its first Nuclear weapon.
1962 Cuban missile crisis brings world to brink of nuclear war.
1963 U.S., U.K., & U.S.S.R. sign treaty ending above-ground nuclear tests.
1964 China tests its first Nuclear weapon.
1968 59 non nuclear nations join U.S, U.K., & U.S.S.R. in nuclear Non Proliferation Treaty (NPT). Total 187 today.
1972 U.S., U.S.S.R. & 100 other nations sign Biological Weapons Convention. Soviets violate pact.
1972 U.S. & U.S.S.R. sign Anti-Ballistic Missile (ABM) treaty.
1974 India (not party to NPT) tests its first nuclear weapon.
1979 Anthrax spores accidentally released in U.S.S.R. kill at least 68 people.
1980 Smallpox is officially eradicated.
1983-88 Chemical weapons used extensively in Iran-Iraq war; thousands die.
1988 Iraq kills 5,000 Kurds with mustard gas and other chemicals dropped on town of Halabjah.
1991 U.N. orders Iraq to destroy all weapons and related to technology then begins inspections.
1991 Soviet Union dissolves; U.S. starts nonproliferation aid program in former U.S.S.R.
1992 U.S. announces moratorium on nuclear tests.
1993 Chemical Weapons Convention opens for signature.
1995 Religious cult releases Sarin nerve gas in Tokyo subway, killing 12.
1996 All Soviet nuclear weapons in Belarus, Kazakhstan, and Ukraine are transferred to Russia.
1998 Pakistan tests its first nuclear weapon.
1998 Citing lack of cooperation, UN withdraws weapons inspectors from Iraq.
2001 Anthrax spores mailed via U.S. postal system infect 23, killing five.
2002 U.S. withdraws from ABM Treaty to allow development of missile defense.