Battle of Annual
During the Third Rif War in Spanish Morocco between 1921 and 1927, the Spanish Army of Africa dropped chemical warfare agents in an attempt to put down the Riffian Berber rebellion against colonial rule led by guerrilla leader Abd el-Krim. Following the humiliation at the Battle of Annual in 1921, considered as the worst Spanish defeat in the 20th-century, the Spanish army pursued a vicious campaign of retribution involving the indiscriminate and routine dropping of toxic gas bombs targeting civilian populations, markets and rivers.