Chemical weapons have been used in at least a dozen wars since the end of the First World War; they were not used in combat on a large scale until Iraq used mustard gas and the more deadly nerve agents in the Halabja chemical attack near the end of the 8-year Iran–Iraq War. The full conflict's use of such weaponry killed around 20,000 Iranian troops (and injured another 80,000), around a quarter of the number of deaths caused by chemical weapons during the First World War.