During WWII, the Japanese army had a secret biological warfare research unit in Manchuria called Unit 731. Unit 731 was responsible for some of the most notorious war crimes carried out by Japan. General Shiro Ishii was the lead physician of Unit 731.
Biological Warfare was banned by the Geneva protocol of 1925, and General Shiro Ishii thought that since it was banned, it must be effective. Unit 731 conducted a series of cruel experiments in order to test how the human body reacts when subjected to harsh conditions, poisonous substances, and lethal diseases.
On October 4, 1940, the Japanese dropped plague-infected fleas over Quzhou, a small town in western Zhejiang Province. In just one year more than 2,000 people in Quzhou died from this plague. The next year, a railway worker brought the plague from Quzhou to the city of Yiwu, and more than 1,000 people in Yiwu died from this plague within a year.
In 1942 the Japanese also made a series of anthrax and glanders attacks on many villages in the Jinhua area of Zhejiang Province and around 6,000 inhabitants of Jinhua were infected by bacteria from biological weapons. More than 3,000 people died after they got infected.
For over 13 years, the Japanese performed experiments in the Unit 731 Complex. Their activities were ended in 1945 when Russia invaded Manchuria in August. Unit 731 was burned and all evidence was destroyed. General Shiro Ishii and the other workers were never punished for their war crimes.