The AIDS pandemic didn't just happen overnight. The disease, which probably made the leap to humans in the late 19th or early 20th century, had decades of neglect, ignorance, irresponsibility, and homophobia in which to ferment before becoming an all-out pandemic. A little-known illness from the African bush ultimately resulted in a death toll -- now 25 million, and counting -- that rivals our longest, costliest, and bloodiest wars.