Following up on this previous BoingBoing post about reports that white phosphorous (WP) is among the weapons being used by US Marines in Falluja, reader Marty Busse says:
It has a long history of use as a weapon by the US military, and the legal issues around it are rather contentious.
The book A Higher Form of Killing, by Robert Harris and Jeremy Paxman, contains a very small ref to use of WP in WWII, when there was a dispute about its use between the British and the US: the US was not bound by the Geneva Protocol for the Prohibition of the Use in War of Asphyxiating, Poisonous or Other Gases, and of Bacteriological Methods of Warfare (which the British felt use of WP was prohibited by) and the British yielded to the US opinion. (The US didn't ratify that protocol until 1975, but with some reservations on the use of riot control agents: Link.) And this article refers to the current Geneva Protocol on Incendiary Weapons, which the US is not a party to: Link.
I recommend taking a look at A Higher Form of Killing, which contains all sorts of interesting information and a few very neat photos, including one of the massive apparatus used to create anthrax bombs during WWII.
(It also contains a few rather gruesome photos.)
Link to book.
Image: White phosphorous rounds explode on enemy positions north of the Han River prior to U.N. offensive during March 1951. Link