Unchecked proliferation of modern chemical and biological weapons may radically alter the terms of warfare.
Since the end of World War II, the debate over proliferation of weapons of mass destruction has been dominated by discussions of nuclear weapons. The last several years, however, have seen growing concern about chemical and biological weapons. In the years ahead, chemical and biological weapons may, in fact, overshadow nuclear weapons as the primary proliferation issue.
Chemical weapons are poisons that incapacitate, injure, or kill through their toxic effect on the human body. They are generally classified as blister, blood, choking, incapacitating, or nerve agents, depending on which part of the body they are designed to affect. Some chemical agents can be lethal when vaporized and inhaled in amounts as small as a few milligrams.
Biological weapons are living organisms or the byproducts of living organisms used as instruments for waging conflict. In essence, biological warfare is the deliberate spread of disease. Biological weapons generally are categorized as bacteria, viruses, rickettsia, and toxins. As lethal as chemical weapons can be, biological weapons can be many times deadlier pound-for-pound. Laboratory tests on animals, for example, indicated that, if effectively disseminated and inhaled, 10 grams of anthrax spores could produce as many casualties as a ton of chemical nerve agent. 
Chemical and biological weapons are easy and cheap to produce in comparison with nuclear weapons. Illicit chemical and biological weapons programs are difficult to detect since the technology, which is also used for legitimate commercial, medical, agricultural, and other purposes, is readily available. Chemical and biological weapons could also have great strategic impact; for example, an effectively disseminated biological weapon can produce levels of casualties comparable to those of a small nuclear weapon. 
Chemical and biological weapons could become the weapons of mass destruction of choice in the decades ahead, particularly for actors looking for major, but relatively cheap, leverage in pursuit of ambitious goals. Chemical and biological weapons could be very attractive to countries with regional designs against neighbors with limited military capabilities.
But they could also be valuable to such states in a confrontation with a major power like the United States. These weapons would allow even small nations to avoid contesting U.S. conventional military power directly by using an asymmetric strategy that seeks to exploit U.S. vulnerabilities.
The emergence of terrorist groups or fanatical individuals with motivations and world views far different from those of traditional political terrorists increases the risk that non-state actors--that is, those operating on their own without government support--might consider these weapons as a contingency. Indeed, some people contend that bioterrorism is "the single most dangerous threat to our national security in the foreseeable future." 
Ancient Arts of War
The use of chemicals as a weapon of war dates far back in time. Historians noted the use of toxic fumes in conflicts in India as far back as 2000 BC. In 1591, Germans burned combinations of shredded hooves and horns with a fetid gum resin to produce noxious clouds to disrupt enemy forces. Even modern chemical weapons have been around a long time. The British chemist Sir Humphrey Davy prepared the respiratory irritant phosgene in 1811, and the chemical today known as mustard was synthesized in 1854. The most lethal chemical agents, the nerve gases, were initially developed from German research into organophosphorous pesticides in the 1930s. 
Biological weapons also have a long history. An early example of biological warfare can be dated to 1346 at Kaffa--now Fedossia, Ukraine--where plague-ridden corpses of Tartar soldiers were catapulted over the walls of the besieged city. …