Political event
The King of Hyrule determines that they will not keep peace with the Gerudo if they do not agree to erase Magnus from their history, culture, lives, etc.
Believing that Magnus was 1) deeply hated by the gods 2) a figure that would spark another civil war and 3) had technology that was far more powerful than anything the King could compete with 4) Was a being and name so hated by the gods that anything associated with him would turn the gods against Hyrule, the King of Hyrule decrees that anything related to Magnus must be removed from existence. The Gerudo had harbored Magnus and had allowed him to build many structures in their desert. The King demanded that they erase any notable evidence of Magnus's existence. During this time, those loyal to Magnus sought refuge in the Gerudo desert.They knew Magnus had spoken kindly of Vile and the eighth, so they sought her out. They established themselves as the Yiga in the eighth's and Vile's temple. These people were often killed in Gerudo Canyon before they could make it to Vile's refuge. The Gerudo were appalled by these decisions, and the civil war continued with the Gerudo posed against Hyrule.