In 2012, a 20-year moratorium on state employment of chemical weapons use was broken. Since then, there have been more than 200 uses, against civilians, military targets, and political enemies. These attacks have broken norms against the use of weapons of mass destruction and create a gap in the nonproliferation fabric—despite the robust international architecture of laws, treaties, agreements, and norms designed to restrain the proliferation and use of these weapons. Accountability for th...