We know that AIDS ravages bodies. But can the disease topple governments? Some experts fear the infectious epidemic that has already killed 22 million worldwide could also unseat leaders, change borders and threaten global security. The theoretical trail of wreckage goes something like this: AIDS decimates military, police and peacekeeping forces, erodes social services and local institutions and incites internal unrest by eroding faith in government. Ultimately, the epidemic could leave power vacuums in hardest-hit countries, making nations vulnerable to aggressors and terrorists. "If you simply sit back and watch these places become unhinged, particularly in weak states to...