For centuries, following bloody conflicts, military leaders acknowledged that some weapons were simply too awful to be used, but those same militaries generally continued to use them.

The first world war (WWI) saw the successful deployment of chemical weapons on a massive scale for the first time. The horror of millions of dead soldiers, in trenches and on battlefields, shocked nations into signing in 1925 the Geneva Protocol pledging to refrain from the use of chemical and biological weapons in future wars.

Over the past century, the weapons that cause "unjustifiable" suffering in an indiscriminate and "unpredictable" manner have been subject to multilateral treaties that aim to disarm countries that possess them and control or ban the use of these weapons altogether.

While some may feel sceptical that these efforts to disarm the world are effective, and challenges to disarmament remain, the disarmament treaties serve a key role in the regulation and reduction in stockpiles, as well as in the testing and use of certain weapons in conflicts. The use of banned weapons constitutes a war crime.

Disarmament treaties over the past century

Nuclear weapons treaties (14) Date Treaty Description 1959 Antarctic Treaty A treaty that sets aside Antarctica as a scientific preserve, establishes freedom of scientific investigation and bans military activity on that continent. 1963 Partial Test Ban Treaty The Partial Test Ban Treaty prohibited all test detonations of nuclear weapons except for those conducted underground. 1967 Outer Space Treaty The treaty provides guidelines for the exploration and use of outer space, the Moon and other celestial bodies. Parties will refrain from placing in orbit around the Earth any objects carrying nuclear weapons or any other kinds of weapons of mass destruction, install such weapons on celestial bodies, or station such weapons in outer space in any other manner. 1968 Treaty of Tlatelolco A treaty to prevent the spread of nuclear weapons and weapons technology, to promote cooperation in the peaceful uses of nuclear energy and to further the goal of achieving nuclear disarmament and general and complete disarmament. 1968 Nuclear-Weapon-Free Zone A treaty for the Prohibition of Nuclear Weapons in Latin America and the Caribbean. 1971 Seabed Treaty A treaty on the Prohibition of the Emplacement of Nuclear Weapons and Other Weapons of Mass Destruction on the Sea-Bed and the Ocean Floor and in the Subsoil Thereof. 1979 Moon Agreement An agreement stating the Moon should be used for the benefit of all states and all peoples of the international community. It also expresses a desire to prevent the Moon from becoming a source of international conflict. Bans any military use of celestial bodies, including weapon testing or as military bases. 1985 Treaty of Rarotonga The treaty bans the use, testing, and possession of nuclear weapons within the borders of the "South Pacific Nuclear Free Zone". 1995 Treaty of Bangkok A treaty between 10 Southeast Asian member-states under the auspices of the ASEAN: Brunei Darussalam, Cambodia, Indonesia, Laos, Malaysia, Myanmar, Philippines, Singapore, Thailand, and Vietnam. It obliges its members not to develop, manufacture or otherwise acquire, possess or have control over nuclear weapons. 1996 Comprehensive Nuclear-Test-Ban Treaty A treaty that bans all nuclear explosions, for both civilian and military purposes, in all environments. 1996 Treaty of Pelindaba The African Nuclear Weapon Free Zone Treaty, it prohibits the research, development, manufacture, stockpiling, acquisition, testing, possession, control or stationing of nuclear explosive devices in the territory of parties to the Treaty and the dumping of radioactive wastes in the African zone by Treaty parties. 2005 Nuclear Terrorism Convention A United Nations treaty designed to criminalise acts of nuclear "terrorism" and to promote police and judicial cooperation to prevent, investigate and punish those acts. 2006 Treaty on a Nuclear-Weapon-Free Zone in Central Asia The treat is a legally binding commitment by Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan not to manufacture, acquire, test or possess nuclear weapons. 2017 Treaty on the Prohibition of Nuclear Weapons At treaty that provides for a time-bound framework for negotiations leading to the verified and irreversible elimination of its nuclear weapons programme for signatory states. Chemical weapons treaties (2) Date Treaty Description 1919 Treaty of Versailles Contains provisions banning the use of poison gas. 1993 Chemical Weapons Convention The Convention of the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction. Biological weapons treaties (1) Date Treaty Description 1972 The Biological Weapons Convention The Convention on the Prohibition of the Development, Production and Stockpiling of Bacteriological (Biological) and Toxin Weapons and on their Destruction. Conventional weapons treaties (8) Date Treaty Description 1980 Convention on Certain Conventional Weapons A convention that prohibits or restrict the use of certain conventional weapons which are considered excessively injurious or whose effects are indiscriminate. 1990 Treaty on Conventional Armed Forces in Europe A treaty that established comprehensive limits on key categories of conventional military equipment in Europe (from the Atlantic to the Urals) and mandated the destruction of excess weaponry. 1997 Anti-Personnel Mine Ban Convention Convention on the Prohibition of the Use, Stockpiling, Production and Transfer of Anti-Personnel Mines and on their Destruction, an international agreement that bans antipersonnel landmines. 1997 Inter-American Convention on Firearms A convention that establishes a regional standard for the control of the illicit manufacturing and trafficking in firearms. 1999 Inter-American Convention on Transparency A convention that establishes voluntary annual reporting by member-states on their arms imports, exports, and procurement through national production of any of seven categories of weapons - battle tanks, armoured combat vehicles, large-calibre artillery, combat aircraft, attack helicopters, warships, and missiles and missile launchers. 2008 Convention on Cluster Munitions An international treaty that prohibits the use, transfer, and stockpiling of cluster bombs - a type of explosive weapon which scatters submunitions ("bomblets") over an area. 2010 Kinshasa Convention The Central African Convention for the Control of Small Arms and Light Weapons, their Ammunition, Parts and Components that can be used for their Manufacture, Repair or Assembly. 2013 Arms Trade Treaty A multilateral treaty that regulates the international trade of conventional weapons for the purpose of contributing to international and regional peace; reducing human suffering; and promoting cooperation, transparency, and responsible action by and among states. Multiple weapons treaties (4) Date Treaty Description 1899 1st Peace Conference at the Hague A series of treaties, including the Prohibition of the Discharge of Projectiles and Explosives from Balloons or by Other New Analogous Methods; Prohibition of the Use of Projectiles with the Sole Object to Spread Asphyxiating Poisonous Gases; Prohibition of the Use of Bullets which can Easily Expand or Change their Form inside the Human Body. 1907 2nd Peace Conference at the Hague A series of treaties, including: Convention relative to the Laying of Automatic Submarine Contact Mines; Concerning the Prohibition of the Use of Projectiles with the Sole Object to Spread Asphyxiating Poisonous Gases; Declaration Prohibiting the Discharge of Projectiles and Explosives from Balloons. 1925 Geneva Protocol The Protocol for the Prohibition of the Use in War of Asphyxiating, Poisonous or other Gases, and of Bacteriological Methods of Warfare. 1976 Environmental Modification Convention A convention prohibiting the military or other hostile use of environmental modification techniques having widespread, long-lasting or severe effects - includes any technique for changing - through the deliberate manipulation of natural processes - the dynamics, composition or structure of the Earth, including its biota, lithosphere, hydrosphere and atmosphere, or of outer space.

2017 UN Disarmament Week

From October 24-30, the United Nations observes Disarmament Week. During this period, member-states are invited to "highlight the danger of the arms race, propagate the need for its cessation and increase public understanding of the urgent tasks of disarmament". These efforts include the regulation and banning of weapons of mass destruction (WMDs), including nuclear, chemical and biological weapons, as well as conventional weapons (CW) such as laser weapons - both incendiary and blinding, landmines and certain types of munitions, among others.

The following five cases demonstrate the role international treaties play and how effectively they regulate the use and production of these weapons.

Biological weapons (WMD)

Biological weapons have not been used by states during conflict since World War I, after the Geneva Protocol was signed in 1925. The 1972 Biological Weapons Convention further solidified state commitment to their prohibition in war. However, because the treaty does not provide any monitoring or verification mechanisms, many countries continue research and stockpiling activities. Biological toxins used for weapons include bacteria, viruses and fungi. Notorious historical examples of toxins used in times of war include: plague, smallpox, faeces, anthrax and cholera, among others.

Major uses of biological weapons Date Event Description Pre-19th century Wars Used globally to cause injury and weaken enemies through contaminated water, poisoned bullets, intentional spreading of disease such as smallpox and plague among others. 1914-1918 World War I Germany used bio-agents to sabotage the enemies by spreading anthrax through animals. 1925 Treaty Geneva Protocol banned use of chemical and biological toxins in war. 1939-1945 World War II No combat use. Japan experimented biological weapons on prisoners, killing about 3,000 people. Nazis also conducted such experiments in Germany. 1972 Treaty Biological Weapons Convention bans the use, production and posession of biological weapons. 1945-present Research and Development No combat use since WWI, but most countries are believed to possess and continue stockpiling biological weapons.

Chemical weapons (WMD)

After the World War I massacres and the consequent signing of the Geneva Protocol, warring factions became hesitant and did not use chemical weapons on battlefields during the second world war (WWII). Nazis did, however, use them to murder millions of Jews in gas chambers. Chemical weapons have been used in many conflicts thereafter. The 1993 Chemical Weapons Convention implemented verification mechanisms that have seen through the voluntary destruction of 93 percent of the global stockpiles by signatory states. Furthermore, as using chemical weapons is a war crime, factions that resort to using them, do so in secret and deny having done so.

Major uses of chemical weapons Date Event Description 1914-1918 World War I 190,000 tonnes produced by all parties involved in the war. Casualties: 1.2 million wounded, 100,000 dead. 1925 Treaty Geneva Protocol banned use of chemical and biological toxins in war. 1935-1936 Second Italo-Ethiopian War Used by Italian forces against Ethiopians. Casualties: 15,000 people killed or injured. 1939-1945 World War II Tonnes of weapons produced and stockpiles increased by all parties participant in war, yet no combat or battlefield uses. However, Nazi forces used chemical poisons in gas chambers to murder millions of Jews and other peoples. 1965-1975 Vietnam War 73 million litres of chemical agents were used during the war. Most notably the US used Agent Orange against the Vietnamese. Casualties ranged from 2.1 to 4.8 million people, spanning decades after the war; environmental damage spanning 31,000sq km. 1980-1988 Iran-Iraq War Used by Iraqi forces, with casualties of upto 100,000 Iranians. In the Halabja Kurdish village attack, between 3,200 and 5,000 people were killed, and between 7,000 and 10,000 were injured. 1993 Treaty Chemical Weapons Convention signed. 2011-present Syrian civil war Used by Syrian government on rebels and civilians. Hundreds of casualties reported over various incidents.

Nuclear weapons (WMD)

Nuclear weapons were only used in wartime once, when the US bombed the Japanese cities of Hiroshima and Nagasaki during World War II. A nuclear arms race followed, during the Cold War period between Western and Eastern bloc countries, mainly the US and USSR, during which there was an exponential growth in testing and stockpiling of nuclear weapons. The numerous treaties signed in this period have ended nearly all testing, and stockpiles have been reduced from over 60,000 in 1985 to about 15,000 currently, with a commitment to reduce this number to about 7,000 by 2022 by signatory countries.

The International Campaign to Abolish Nuclear Weapons (ICAN) was awarded the 2017 Nobel Peace Prize in recognition of their work to this end.

Anti-personnel landmines (CW)

Landmines that target people have been used throughout history, but most widely during World War II. They cause death and crippling injuries to civilian populations long after conflicts have been settled. The 1997 Mine Ban Treaty, or Ottawa Treaty, set to eliminate the production and use of landmines. Since the implementation of the treaty, 159 signatory states have declared they have no stockpiles, having destroyed a combined 51 million mines. Post-conflict demining is an ongoing challenge for many of the most heavily mined countries, including Bosnia, Cambodia, Afghanistan, Myanmar and Egypt, as is the continued use of mines by non-signatory states.

The International Campaign to Ban Landmines (ICBL) was awarded the 1997 Nobel Peace Prize "for their work for the banning and clearing of anti-personnel mines".

Although stockpiles of traditional landmines have decreased, deaths and injuries have increased in recent years, due to the increased use of improvised explosive devices by non-state groups.

Cluster munitions (CW)

Cluster munitions, which eject small bomblets over a wide area after being released, were first used by the Soviet Union during World War II and have been used in nearly every bombardment campaign since. Civilians constitute 98 percent of casualties, falling victim both to the wide swaths of damage in the target area during an attack and to unexploded remnants - bomblets that land, but do not detonate - in the aftermath of the attack. While 108 countries have signed the 2008 Convention on Cluster Munitions, about half the world, including Saudi Arabia and Syria, have not and continue using them in current wars.