War directs scarce resources away from health and other human services, and often destroys the infrastructure of these services; it also facilitates the spread of disease. Since the early 1970s, another major threat has emerged for health care systems. Military attacks on medical personnel and medical facilities, though prohibited under international humanitarian law, have reached alarming proportions throughout the world.

One recent example occurred in Kosovo during the Yugoslav government's offensive against ethnic Albanian rebels in the summer and fall of 1998, when troops destroyed tens of thousands of buildings, including health clinics, and displaced hundreds of thousands of civilians who sought shelter in the surrounding mountains and forests. Aid officials estimated that about twenty doctors were arrested by Serbian special police or fled the country and that hundreds of civilians may have died because of the collapse of the health care system. After the assualt, a climate of fear descended on the few health care workers who remained in the war zone. Several doctors said that, in spite of their ethical obligations to treat all those in need, they were afraid to provide medical care because it could serve as a pretext for government police to arrest them.

Attacks on medical facilities are prohibited under the Geneva Conventions of 1949 and the 1977 Additional Protocols. These instruments provide that warring factions have an obligation to protect civilians, the sick and wounded, combatants who are hors de combat, and medical and religious personnel. All sides in a conflict must protect certain objects from damage, including hospitals and other medical facilities, ambulances, and equipment bearing the Red Cross or Red Crescent symbol that have removed wounded from the field; transport and facilities used by humanitarian and relief agencies; and objects indispensable to the survival of the civilian population, such as crops, livestock, and drinking water installations.

But the reality is very different. In contemporary conflict, medical personnel and patients are assaulted, abducted, tortured, or murdered. Ambulances can become the target of mortar and sniper fire. Medical transports carrying vital medical supplies and food may be shelled or prevented from reaching towns and cities under siege. All of these acts may be considered grave breaches of the Geneva Conventions and Additional Protocol I or crimes against humanity. As refugees flee to safety, they congregate in makeshift camps where the combination of fatigue, malnutrition, unsanitary conditions, and overcrowding often sends diseases like cholera and measles on a killing spree.

During the 1994 genocide in Rwanda, military and militias known as Interahamwe (those who attack together) entered dozens of hospitals and clinics, murdering and maiming patients and staff. One of the most horrific incidents took place in the university town of Butare, where machete-wielding militiamen slaughtered twenty-one children who had been evacuated to a Red Cross orphanage.

During the 1980s, Mozambique National Resistance (RENAMO) guerrillas in Mozambique ransacked over one thousand primary health centers, representing 48 percent of the national total, leaving 2 million people without access to health care.

In Bosnia-Herzegovina, where armed conflict was marked by almost every conceivable violation of medical neutrality, Sarajevo's main medical center, the Kosevo Hospital, was struck by at least 172 mortar shells in 1992 and early 1993. The most flagrant attack on the hospital complex took place in May 1992, when Bosnian Serb forces, at close range, repeatedly shelled the Children's Clinic and the adjoining Obstetrical and Gynecological Hospital, forcing staff to evacuate seventeen newborns (many removed from their incubators and without supplemental oxygen) and thirty-three older children. Nine of the babies later died for want of heat and oxygen.

Even without coming under direct attack, health care systems have to cope with an enormous burden in wartime. Hospitals in or near war zones are usually understaffed and have few, if any, orthopedic surgeons, let alone general surgeons with extensive experience treating blast-related injuries. Patients with mine blast injuries often require twice as much blood as patients wounded by other munitions. Many—if not most—mine amputees will need to be fitted with some kind of prosthetic, which will need to be replaced every three to five years. And after the fighting stops, the pressures continue. Antipersonnel mines place a tremendous burden on the health care systems in postwar countries. Victims of mine blasts are more likely to require amputation and remain in the hospital longer that those wounded by other munitions. Unexploded ordinance and small antipersonnel mines strewn along footpaths, rice paddies, riverbeds, and around villages continue to maim and kill the children and grandchildren of the soldiers who laid them.

The other threat to health care systems is disease. Throughout history, conquering armies have not only killed and maimed their enemies, they have brought with them communicable diseases, such as the bubonic plague, tuberculosis, measles, smallpox, chicken pox, whooping cough, mumps, and influenzas, which, when invading a human population without any previous exposure to them, are likely to kill a high proportion of those who fall sick. In the early 1500s, during the conquest of Mexico, millions of Aztec Indians died of chicken pox introduced by Hernan Cortés and his men. Two centuries later, British troops in the American colonies on at least one occasion during the Indian uprising of 1763, known as Pontiac's Rebellion, deliberately sent blankets infected with smallpox to Shawnee and Delaware Indians. During the Revolutionary War, American troops also accused the British of spreading smallpox by forcing infected people out of cities with the design of spreading the disease among American soldiers.