During the civil war in Syria more than 100,000 civilians have been killed but only the use of chemical weapon triggered a response from the EU and the United States.

This raised a moral question: Why mass killing with "conventional" weapons is being ignored by the rest of the world, whilst the use of chemical weapons draws immediate attention and the need for international action.

What is the Chemical weapons taboo? Why was it created and how? I'll try and find some answers.