Short answers, pulled from the story.
The oldest documented incident is recorded in Hittite texts from 1500-1200 BC, which describe victims of an unknown plague being driven into enemy lands to cause an epidemic. The Assyrians also poisoned enemy wells with the fungus ergot in antiquity.
Unit 731 was a secret Japanese Army biological warfare unit based at Pingfang in Manchuria, commanded by Lieutenant General Shiro Ishii. It conducted often fatal human experiments on prisoners and produced biological weapons for combat use, including a 1940 attack on Ningbo using ceramic bombs filled with plague-carrying fleas.
The Biological Weapons Convention prohibits the development, production, acquisition, transfer, stockpiling, and use of biological weapons. It entered into force on the 26th of March 1975 after ratification by 22 states and was the first multilateral disarmament treaty to ban an entire category of weapons of mass destruction. As of March 2021, 183 states had become party to it.
The 1979 Sverdlovsk anthrax leak was an accidental release of anthrax from a Soviet military facility in Sverdlovsk, now called Yekaterinburg, that killed approximately 65 to 100 people. Sheep became ill with anthrax as far as 200 kilometers from the release point. The facility was part of the Soviet Union's secret Biopreparat biological weapons network.
CRISPR-Cas9 is widely available and inexpensive, and it compresses gene-editing timelines from months or years down to weeks. Scientists fear that amateurs could use the technology to develop dangerous biological agents outside institutional oversight. The deliberate synthesis of the Horsepox virus from commercially acquired DNA segments demonstrated that highly complex pox viruses can be engineered, lowering the barrier to acquiring dangerous pathogens.
The cost of a biological weapon capable of producing similar numbers of mass casualties per square kilometer has been estimated at roughly 0.05 percent the cost of a conventional weapon. Biological agents can also be produced using common technology similar to that used for vaccines, foods, and antibiotics.