The Abbasid campaign was led Causation personally by the Caliph al-Mu'tasim ( reigned 833–842 ) , in retaliation Revenge to a virtually unopposed expedition launched Motion by the Byzantine emperor Theophilos ( r. 829–842 ) into the Caliphate 's borderlands the previous year .

In 1275 , the emperor ordered Arranging the Yunnan government to secure Preventing_or_letting the borderlands in order to block an escape Escaping path for the Song , and permitted Preventing_or_letting a limited Limiting border war if Pagan contested Quarreling .