Mr. Derbyshire is right: AIDS is a disease, not a weapon or a state actor. But it is not the case that AIDS relief in Africa has no connection to our national interest.

At an individual level, AIDS is not a threat to U.S. security. But as a contributing factor to state failure in Africa, AIDS, much like poverty, has found itself on our national-security agenda. The Clinton administration acknowledged this, President Bush emphasized it, and President Obama is rightfully following suit.

On the national level, the fight against HIV/AIDS weakens a state’s capacity to provide security, health care, and education to its population. It also weakens the capacity of African military and peacekeeping forces. According to the Joint United Nations Program on HIV/AIDS (UNAIDS), sexually-transmitted-infection (STI) rates among armed forces are generally 2 to 5 times higher compared with civilian populations during peacetime; in times of conflicts, they can be more than 50 times higher.

Describing the impact of HIV on Africa’s security forces requires no exaggeration. In Zambia, AIDS-related illnesses have reportedly killed more military personnel since 1983 than have been killed in all of Zambia’s military operations combined. In Uganda, the national-security force has reportedly lost more soldiers to AIDS than to two decades of war with the Lord’s Resistance Army.

The economic impact of the disease on African forces is equally debilitating: the loss of trained personnel, prolonged absences, illnesses, and the cost of treatment to soldiers.

Why does this matter to the U.S.? Because the human and economic costs of AIDS take away from the already-limited resources that African states have to devote to domestic security. And the weaker a state’s security forces are, the likelier it is that terrorist groups will be able to grow undetected inside their borders. The devastating effect of AIDS on African security forces also works against the U.S.’s considerable investments in the training of these forces in global anti-terrorism efforts. AIDS weakens the capacity of many African forces to participate in regional peacekeeping operations, some of which involve fighting terrorists groups. In Somalia, for example, we rely on an African Union force made up of Ugandan and Burundian soldiers to keep the al-Qaeda-linked terrorist group al Shabaab from taking over Somalia’s capital.

Morality, generosity, and humanitarianism aside, there are pragmatic reasons why three consecutive U.S. administrations have linked AIDS relief to our national interests.

— Emily Putze is a research assistant at the American Enterprise Institute.