In 1995, Japan’s Aum Shinrikyo cult turned the nerve agent on a small number of its members, whom leaders believed to be police informants. On a larger scale, VX was one of the chemical weapons deployed in the Iran-Iraq war. The Kim Jong Nam case, though, would be the first VX assassination on record, and the first time chemical weapons were used to that end since a ricin pellet—fired from an umbrella gun—took Bulgarian dissident Georgi Markov’s life in 1978.
“That this particular chemical weapon would be used in a political assassination in a third country is very alarming. It’s a red line,” says Ingelsby. “It should be considered a new threshold that’s been crossed in terms of unconventional weapons.”
Those norms matter. After decades without any nation deploying chemical weapons, Syria used sarin and chlorine gas. If a nation-state such as North Korea uses VX once, they or other actors may well do it again.
https://www.wired.com/2017/02/using-vx-nerve-agent-kill-kim-jong-nam-crossed-red-line/