Genocide and crimes against humanity can be carried out with machetes. They can be carried out with nuclear weapons. It appears, however, that in the current state of international law, using a nuclear weapon on people may not, in itself, be genocide, a crime against humanity, or otherwise absolutely forbidden.

The Nuclear Age arrived in the desert near Los Alamos, New Mexico, on July 16, 1945, with the first nuclear test detonation. That same year, the bombs were dropped from U.S. planes on the Japanese cities of Hiroshima, on August 6, and Nagasaki, three days later. Hiroshima and Nagasaki have been the only uses of nuclear weapons in armed conflict.

Subsequently, the Soviet Union, the United Kingdom, France, and China became avowed members of the Nuclear Club. The United States and the Soviet Union tested hydrogen devices of ever more awesome power. Israel is widely believed to have nuclear weapons. South Africa probably...