hi! you may be interested in some earlier posts
Historical rules/laws of war - /u/blatherskiter discusses ancient precedents
What is the history of the laws/ethics of military warfare? How have they evolved over the years? - /u/georgy_k_zhukov and /u/kwgoodlet continue the story to the turn of the century
What is the earliest known instance of a type of weapon/warfare being "banned" by both sides of an armed conflict? - /u/georgy_k_zhukov gives a quick summary of banned weapons
Before the modern period, were there ever any "forbidden techniques" of combat? - /u/ny-batteri expands further on crossbows
Since the Chemical Weapons Convention wasn't signed until 1993, why weren't chemical and biological weapons used by the incredibly desperate Axis powers in WWII? - a discussion on chemical weapons
... and there are several more posts on the use of chemical and biological weapons
of possible tangential interest