Did, as is often claimed by "lefties," the U.S. Army distribute smallpox-laden blankets to Native tribes during our wars of conquest? This is a common story I have heard and read in various sources throughout the years.
But: is this story "true"? It turns out that the infamous Ward Churchill was one of the major proponents of the biological warfare argument-and his research may have been fabricated. http://hal.lamar.edu/~BROWNTF/Churchill1.htm
(Not to deny our genocidal history, but...)