The US fire bombing of Japanese cities killed more civilians than the Hiroshima and Nagasaki bombs combined, including those that have died since. The Japanese use of biological warfare against China and Manchuria killed a large, but indefinite, number of people -- Chinese, Manchurian, and Japanese. By various means the Third Reich was directly responsible for the deaths of at least 16,000,000 people. Stalin was responsible for the deaths of about 8,000,000, including the German soldiers who surrendered and were then marched off to Siberia. Pol Pot killed two or three million in Cambodia. The Hutu/Tutsi genocide in Rwanda killed -- how many? How many in Serbia? How many in Sudan? How many in Armenia? How many?

We don't need superweapons to kill off our neighbors. We do a pretty damned good job with what we have.