Because the definition for weapons of mass destruction, or WMDs, is so broad, the scope of the problem of these weapons is similarly one that involves many security risks, preventative measures, and multilateral agreements. While the degree of damage, that nuclear bombs and missiles are capable of doing is clearly evidenced by their use in Hiroshima and Nagasaki, there is some uncertainty as to how much devastation chemical and biological weapons can cause. However the amount of devastation and lasting effects of the damage caused by the use of a nuclear weapon is much more detrimental than the use of a chemical or biological weapon. Also, when talking about the extent of damage caused by weapons of mass destruction, it is important to distinguish a dirty bomb from a nuclear bomb or missile; the latter being about a thousand times more deadly.
Since their development during WWII, atomic weapons have been a controversial and risky topic. Yet the fear of one state developing them (Nazi Germany) led another (the United States) to began developing them as a counter measure. Over the course of the second half of the 20th century nations all over the nation had been developing and stockpiling nuclear weapons. During the Cold War the prospect of nuclear war was a considerable threat; the point when the threat of nuclear attack was at its highest was during the Cuban Missile Crisis when the U.S.S.R. threatened the U.S. will a nuclear strike. Fortunately, with the end of the Cold War, the risk of nuclear war between two of the world’s super powers has significantly decreased. Now, and even during the Cold War, there have been initiatives to curtail the spread of nuclear arms; one such example of a multilateral treaty is the Nuclear Non-Proliferation Treaty. In a post-Cold War era, there have been several non-governmental initiatives to promote nuclear disarmament throughout the world. A notable global initiative is Global Zero run by former queen of Jordan, Queen Noor. The most recent case of a potential nuclear strike was when Israel declared that it would attack Iran due to the ongoing threats the latter was making and the hypothesis of Iran's nuclear capability.
Transitioning to the other forms of WMDs- chemical and biological weapons, they have not been used on a large scale by governments or non-governmental groups outside of warfare. Chemical weaponry can range from anything from mustard gas to phosphorous bombs. Biological weaponry are most commonly viruses that are released into the public via air or water supply. One instance of the use of a biological agent being used as a weapon was in 2011 when an outbreak of smallpox occurred in the U.S.
For more information on WMDs and their uses and classifications here are some links used in the research: