Biological warfare is defined as the use of biological weapons such as pathogens, toxins, and/or infectious agents by one sovereign state or entity against another in order to achieve strategic advantages or political hegemony. More specifically, "bioterrorism" is the intentional dissemination of biological agents.
In 1972, the Biological Weapons Convention, which has today been ratified by 183 sovereign states (most recently Tanzania in August 2019), was created in order to prevent the mass production, systematic stockpiling, and widespread use of biological weapons by nations against one another.
While the event of the use of a nuclear weapon would be largely confined to one particular area, biological agents have the potential to spread undetected until a significant number of individuals have been affected. They are also relatively cheap compared to conventional weapons of the nuclear or chemical variety, and experimentation on biological agents by terrorist groups have proven to become a headache for governments and intelligence agencies worldwide.
Entomological warfare (use of insects) and gene-editing are two subsets of biological warfare that can have disastrous consequences. The use of invasive species in the form of insects can damage crops, reduce populations of agriculture-aiding insects, and interrupt supply lines by drastically changing agricultural output. Gene-editing and synthetic biology could be used to render vaccines ineffective, create increased resistance by strains of bacteria or viruses to antibiotics and other medical treatments, or influence the capability of certain pathogens and parasites to affect large populations of humans.
The use of biological weapons has been rendered a crime under the Biological Weapons Convention of 1972, the Geneva Protocol, and international law concerning war crimes, human rights, genocide, and/or armed conflict.