Weapon of Mass Destruction (WMD): A weapon or device that can kill or harm on a large scale.

There are three main categories of WMD:
- Nuclear: the atomic bomb.
- Biological: the use of pathogens, such as Anthrax.
- Chemical: the use of chemicals, such as gas.
Many people condemn the use of WMD, however, others point out that there are some benefits.
People who criticise them claim:
- Use of them can never meet the conditions of the just war theory.
- Too many innocent civilians are killed.
- Countries who keep supplies of them can become too powerful and dangerous.
However, others claim that, whilst not ideal, WMD can have advantages:
- They offer a quick way to win a war, ending it earlier, leading to fewer lives lost. An example of this is when World War II was brought to a close after atomic bombs were dropped on Hiroshima and Nagasaki.
- Fewer lives are lost on the side of the attackers.
- They can act as a deterrent to other nations who are less willing to go to war with a country that has them.