History of chemical warfare in the context of "Weapons of Mass Destruction"

The use of toxic chemicals as weapons dates back thousands of years, but the first large-scale use of chemical weapons was during World War I. They were primarily used to demoralize, injure, and kill entrenched defenders, against whom the indiscriminate and generally very slow-moving or static nature of gas clouds would be most effective. The types of weapons employed ranged from disabling chemicals, such as tear gas, to lethal agents like phosgene, chlorine, and mustard gas. These chemical weapons caused medical problems. This chemical warfare was a major component of the first global war and first total war of the 20th century. Gas attack left a strong psychological impact, and estimates go up to about 90,000 fatalities and a total of about 1.3 million casualties. However, this would amount to only 3–3.5% of overall casualties, and gas was unlike most other weapons of the period because it was possible to develop countermeasures, such as gas masks. In the later stages of the war, as the use of gas increased, its overall effectiveness diminished. The widespread use of these agents of chemical warfare, and wartime advances in the composition of high explosives, gave rise to an occasionally expressed view of World War I as "the chemist's war" and also the era where weapons of mass destruction were created.

The use of poison gas by all major belligerents throughout World War I constituted war crimes as its use violated the 1899 Hague Declaration Concerning Asphyxiating Gases and the 1907 Hague Convention on Land Warfare, which prohibited the use of "poison or poisoned weapons" in warfare. Chemical weapons in World War II saw widespread use by Germany during the Holocaust and by Japan against China. Battlefield use against Western Allies was prevented by deterrence.

A weapon of mass destruction (WMD) is a biological, chemical, radiological, nuclear, or any other weapon that can kill or significantly harm many people or cause great damage to artificial structures (e.g., buildings), natural structures (e.g., mountains), or the biosphere. The scope and usage of the term has evolved and been disputed, often signifying more politically than technically. Originally coined in reference to aerial bombing with chemical explosives during World War II, it has later come to refer to large-scale weaponry of warfare-related technologies, such as biological, chemical, radiological, or nuclear warfare.

The histories of biological and chemical warfare date from antiquity to the modern period, with toxic gases used on a vast scale in World War I. In the 20th century, nuclear weapons were first developed, and were used in war twice, in the atomic bombings of Hiroshima and Nagasaki. Biotechnology allowed for the enhancement of pathogens as weapons, and advanced chemical weapons such as nerve agents were developed. Radiological weapons have never been used or mass-produced.

Ōkunoshima (Japanese: 大久野島) is a small island in the Inland Sea of Japan. It is considered to be part of the city of Takehara, Hiroshima Prefecture. It is accessible by ferry from Tadanoumi and Ōmishima. There are campsites, walking trails and places of historical interest on the island. It is often called Usagi Shima (うさぎ島, "Rabbit Island") because of the large population of free-ranging domestic rabbits that roam the island. The rabbits have been habituated and will approach humans.

Ōkunoshima played a key role during the Second Sino-Japanese War as a poison gas factory for much of Japan's chemical warfare carried out in China.