The History of Biological Warfare

CATAPULTING PLAGUE-INFECTED CORPSES over city walls. Poisoning water supplies with animal carcasses. Engineering anthrax into aerosol spray cans. Biological warfare is one of humanity's oldest and most persistent strategic ideas, and the gap between the ancient versions and the 20th-century programs is less about the concept than about the technology available to execute it.

What makes biological warfare uniquely disturbing is that it weaponizes something that exists independently and unpredictably. A sword kills who you aim it at. A pathogen kills who it reaches, which is not always who you intended. The history of biological warfare is also, therefore, a history of unintended consequences, weapons that turned back on their users, and strategic calculations that underestimated what happens when you release something you can't fully control.

Ancient and Medieval Biological Attacks

The earliest documented instance of what might be called biological warfare is disputed but appears in the Hittite texts from around 1400-1200 BCE. Hittite records describe driving diseased animals, rams and donkeys are mentioned, into enemy territories to spread disease. Whether this was a deliberate strategic weapon or more of an opportunistic nuisance tactic is unclear, but the intent to harm through disease transmission was apparently present.

Greek and Roman sources describe the use of poisoned wells and water supplies during sieges. This was strategically rational from a siege perspective: a city with contaminated water would surrender faster. The Assyrians reportedly used rye ergot to poison enemy wells, though the attribution is uncertain. What is clear is that the idea of attacking enemies through disease or contamination was present in military thinking across the ancient world.

The most famous medieval incident is the Siege of Caffa in 1346. Caffa was a Genoese trading post in Crimea. A Mongol army besieging the city was struck by plague, the Black Death that was moving westward through Asia. The Mongol commander, reportedly Jani Beg, ordered the corpses of plague victims catapulted over the walls into the city. The Genoese defenders fled by sea. Historians have debated whether this event actually introduced plague to Europe (plague was almost certainly spreading through multiple routes simultaneously), but it is the most clearly documented attempt in history to use an epidemic as a weapon.

During the wars between Native American populations and European settlers in North America, there are documented instances of smallpox-contaminated blankets being distributed to Native American populations. The most clearly documented case is from the siege of Fort Pitt in 1763, during Pontiac's War, when a British officer's journal records giving smallpox-contaminated blankets from a military hospital to Delaware tribal leaders who had come to negotiate. Whether this caused a subsequent smallpox outbreak in the region is debated, but the intent was explicitly recorded.

World War I: The Institutionalization of Biological Weapons

The First World War saw the first state-sponsored biological weapons program in the modern sense. Germany ran a covert operation to infect Allied horses and mules with anthrax and glanders, a bacterial disease that affects equines, in several neutral countries including Argentina, Romania, Spain, and the United States. The goal was to disrupt Allied supply chains that depended heavily on horse transport.

The German saboteurs used culture vials concealed in ordinary containers. Operations were mounted at ports in several countries. The American operation targeted horses and mules being shipped to Europe and was run partly out of a base in Mexico. The effectiveness of the program is debated, but the institutional infrastructure it created, a state military program for developing and deploying biological agents, was the model that the 20th century's much larger programs followed.

Japan's Unit 731

The most extensive biological weapons program in history prior to the Cold War was run by the Imperial Japanese Army in occupied Manchuria between 1932 and 1945. Unit 731, based at a facility near Harbin, was a research and development program that used human subjects for experiments on a scale that has few parallels in the history of science.

Prisoners, primarily Chinese civilians and military captives but also Soviet, Korean, Mongolian, and some Allied prisoners of war, were deliberately infected with plague, cholera, typhoid, anthrax, and other pathogens. They were used to test delivery systems, to establish lethal doses, to study how diseases progressed without treatment, and to test vaccines. The prisoners were called "maruta," meaning logs. Estimates of the death toll from Unit 731's experimental program range from 3,000 to 10,000 people, with some estimates higher.

Unit 731 also conducted field operations, dropping plague-infected fleas over Chinese cities and contaminating water supplies. Plague outbreaks in several Chinese cities during the war have been attributed to these operations. The program's commander, Lieutenant General Shiro Ishii, surrendered to American forces in 1945 and negotiated immunity from war crimes prosecution in exchange for turning over Unit 731's research data. The scientists and officers who ran the program were never tried.

The Cold War Arms Race

Both the United States and the Soviet Union ran extensive biological weapons programs during the Cold War. The American program, centered at Fort Detrick in Maryland, was terminated by President Nixon in 1969-1970 in a unilateral decision that surprised even his own military. Nixon concluded that biological weapons were strategically useless because they were too unpredictable, that they undermined arms control negotiations, and that the US nuclear arsenal provided sufficient deterrence. All biological and toxin weapons stockpiles were destroyed. The US signed and ratified the 1972 Biological Weapons Convention.

The Soviet Union signed the same convention and secretly continued its program. Biopreparat, the Soviet biological weapons program, was the largest in history. At its peak in the 1980s, it employed roughly 65,000 scientists and workers across dozens of facilities. It developed weapons-grade versions of anthrax, plague, smallpox, Marburg virus, and other pathogens. It also worked on genetically modified organisms, combining traits from different pathogens to create new variants.

The scope of the Soviet program became known in the West only after the Soviet collapse, primarily through the accounts of defectors including Ken Alibek, who had been deputy director of Biopreparat. The 1979 Sverdlovsk anthrax outbreak, in which an accidental release from a military facility killed at least 66 people (the actual number is disputed and may be much higher), was initially covered up by Soviet authorities and attributed to contaminated meat. The real cause wasn't officially acknowledged until 1992.

After the Cold War: Anthrax Letters and State Programs

The Biological Weapons Convention of 1972 is the primary international legal framework prohibiting biological weapons development, production, and stockpiling. It has been signed by most countries. Unlike the Chemical Weapons Convention, it has no verification mechanism, which means compliance depends entirely on trust and intelligence.

In October 2001, letters containing anthrax spores were mailed to news organizations and US senators in the weeks after the September 11 attacks. Five people died and seventeen were infected. The anthrax was traced to a strain from the US Army Medical Research Institute of Infectious Diseases at Fort Detrick. After years of investigation, the FBI concluded that the likely perpetrator was a US government scientist, Bruce Ivins, who died by suicide in 2008 before charges were filed. The case has remained controversial, with some scientists disputing the FBI's conclusions.

Intelligence assessments have identified ongoing biological weapons programs in several countries in violation of the Biological Weapons Convention. The specific countries and capabilities involved are classified, but the general assessment from multiple Western intelligence agencies is that the norm against biological weapons, while strong, is not universally observed.

Why Biological Weapons Persist

The strategic case against biological weapons is strong: they are unpredictable, they can spread back to the attacker's own population, they are slow-acting compared to conventional weapons, and they are almost impossible to use without clear attribution in the modern era. The public health response to a biological attack would be massive and would generate international pressure.

The case for them, from the perspective of a state or non-state actor with limited resources, is that they are relatively cheap to develop compared to nuclear weapons, they have the potential for mass casualties, and the attribution problem cuts both ways: a covert program is hard to detect until it is used. For an actor that believes it cannot match a stronger adversary in conventional or nuclear terms, biological weapons represent a potential equalizer.

The technology is also becoming more accessible. Advances in synthetic biology and genetic editing tools like CRISPR have lowered the technical barriers to creating dangerous pathogens. The scientific knowledge needed is increasingly published in open literature. Biosecurity experts have been warning for decades that the combination of more accessible biotechnology and persistent political demand for biological weapons represents a growing risk. The history of biological warfare suggests that wherever there is a military problem and a potential biological solution, someone will eventually try it.