[2] These attacks in 1924 marked the first widespread employment of chemical warfare in the post-WWI era[2] and the second confirmed case of mustard gas being dropped from airplanes.
While Spain signed the Geneva Protocol a year later, which prohibited the use of chemical and biological weapons, such use was not illegal in non-international armed conflicts.
[6] The Spanish bombings were covered up but some observers of military aviation, like Pedro Tonda Bueno in his autobiography La vida y yo (Life and I), published in 1974, talked about dropping toxic gases from airplanes and the consequent poisoning of the Rif fields.
Years later, in 1990, two German journalists and investigators, Rudibert Kunz and Rolf-Dieter Müller, in their work Giftgas gegen Abd El Krim: Deutschland, Spanien und der Gaskrieg in Spanisch-Marokko, 1922-1927 (Poison Gas against Abd El Krim: Germany, Spain and the Gas War in Spanish Morocco, 1922-1927), proved with scientific tests that chemical attacks had indeed occurred.
[7] According to Sebastian Balfour, the motivation for the chemical attacks was based primarily on revenge for the defeat of the Spanish Army of Africa and their Moroccan recruits the Regulares[8] at the Battle of Annual on July 22, 1921.
Popular opinion widely blamed King Alfonso XIII who, according to several sources, encouraged General Manuel Fernández Silvestre's irresponsible penetration of positions far from Melilla without having adequate defenses in his rear.
[14] The use of chemical weapons against the Rif was first described in an article of a (now defunct) Francophone daily newspaper published in Tangier called La Dépêche marocaine dated on November 27, 1921.
[25] On February 14, 2007, the Catalan party of the Republican Left (Esquerra Republicana de Catalunya) passed a bill to the Spanish Congress of Deputies requesting Spain to acknowledge the "systematic" use of chemical weapons against the population of the Rif mountains.