[DAS9mm]

It wasn't the Geneva Convention (that deals primarily with the treatment of prisoners) but rather Declaration III of the Hague Convention of 1899 which prohibited the use of "bullets which expand or flatten easily in the human body, such as bullets with a hard envelope which does not entirely cover the core, or is pierced with incisions" in war. It should be noted, however, that the United States did not sign that particular accord and that even amongst signatory nations, it only truly applies when the war is between signatory powers. Given that we didn't sign it and haven't been in a war with a signatory power since WWII, a strong case could be made that the ban on hollowpoints and softpoints does not apply to the U.S., but we go along with it anyway for the sake of political correctness.

An interesting note is that while expanding bullets are banned by the Hague Convention, those designed to fragment (as our own XM193 5.56x45 loading routinely does) or yaw (such as .303 British Mk. VII Ball, 5.45x39 5N7 FMJ, or 7.62x54R 7N1 FMJ) are not prohibited and have been in use by various militaries for over a century.

For those interested, here is a link to Declaration III of the Hague Convention of 1899

Neither the US or Britain are signatories of the Hague Convenventions.